What differences are there between the Gen 4 games?

Question

To elaborate, I’m talking specifically game mechanics. For example, are there any Pokémon level up movesets that change between games? Any bug fixes or balancing to moves or abilities between games? Namely between DP > Plat > HGSS, but in general curious if anyone knows about any overall changes (or lack thereof).

Comments

There definitely were a lot of small changes to things like level up moves and item locations. I don't know if a full list exists anywhere.

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one thing is that Hypnosis had 70% base accuracy in DP and the normal 60% in platinum

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also you could get some moves that weren't available in DP* from move tutors in Platinum

*except as egg moves or from migrating from another game

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https://bulbapedia.bulbagarden.net/wiki/Pok%C3%A9mon_Platinum_Version#Changes_from_Pok.C3.A9mon_Diamond_and_Pearl

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I think what "difference" entails needs to be defined before this question is answered. Obviosuly, there are more difference between DP and HGSS than there are between DP and Pt, but I feel like changes in "game mechanics" needs to be better defined. Like sumwun said, item locations changed, but I personally wouldn't consider that a game mechanic. Are locations of trainers a game mechanic? What if the trainers are in the same location but they variations in Pokemon (or their levels, moves, etc.)? Froggy mentioned move tutors, but I also wouldn't consider that a game mechanic, just something that's available in one game that isn't in another. That being said, there are other features that are available in one game and not another that I WOULD consider game mechanics, such as the Poketch, Pokegear, and Vs. Seeker. Would something like the differences in the Dowsing Machine count, as they have the same use, but the way you use them in DPPt and HGSS are completely different?

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To answer a little bit of what Hellfire Taco is saying, by "game mechanics" I'm specifically referring to things like what I mention in the post: changes to the function of certain moves, level up learnsets, stats and such. Things that usually change between generations. I'm curious if anything like that was altered between games in gen 4, like how Froggyfrogsock mentioned that Hypnosis changed accuracy between DP and Platinum. Looking for more changes like that between DP/Plt/HGSS.

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DP to Pt

> Gameplay
The Wi-Fi area has been enhanced with the Wi-Fi Plaza, which supports up to 20 people at a time. The new area seems to focus exclusively on mini-games, which include Wobbuffet Pop, where players hit a Wobbuffet, Mime Jr. Top, where players can balance Mime Jr. on a ball, and Swalot Plop where players throw Berries at a Swalot machine.
There is a new Key Item called the Vs. Recorder (given by Looker when the player first meets him in Jubilife City), which allows players to record battles in Battle Frontier and Wi-Fi, and share the records with other players at the Global Terminal. Players can also take pictures of their PC boxes and share them with other players in a similar fashion.
The Global Trade System has incorporated an e-mail system that allows players to be notified of completed trades. Notification messages are sent to the player's e-mail account, which can be viewed through the player's PC, mobile phone, or Wii system.
In non-Japanese versions, however, the system was downgraded to Wii messaging only. Thus, in these versions, notification messages are sent and must be viewed through the Wii's Message Board.
The Sinnoh first partner Pokémon and their Evolutions are now allowed in an expanded Amity Square, making a total of 20 Pokémon allowed in the Square.
Over local wireless, there is a new feature called Spin Trade where the player and their friends can put their Pokémon Eggs in and randomly swap. Trainers that obtain Eggs that land on the Bonus Area, the spotted ones, get a Berry too.
HM05 (Defog) is now located inside the Solaceon Ruins instead of the Great Marsh.
The player now receives HM04 (Strength) from Riley on Iron Island instead of in the Lost Tower.
Strength is no longer needed to access Wayward Cave's Hidden Area.
The player can now challenge other Trainers in certain Pokémon Centers. Each Trainer is individually located in front of Pokémon Center desks. These Trainers change location every day.
During a Trainer battle, when the opponent Trainer is about to send out their next Pokémon, the message has changed from "Will <the player> change Pokémon?" in all games up to Diamond and Pearl to "Will you switch your Pokémon?". This was kept in subsequent core series games.
In addition to the Move Tutors in Diamond and Pearl, three new Move Tutors are added: one in Snowpoint City; one other on Route 212; and one more in the Survival Area.
 The accuracy of Hypnosis was changed back to 60. This includes when in a link battle vs Diamond and Pearl.
The game's speed with some features is faster compared to Diamond and Pearl, particularly while surfing and during battles. However, the player still walks slower than in Generation III. The frame rate of Platinum remains 30 frames per second (FPS).
Poffins can be made with other players via Wi-Fi.
A man in the Veilstone Game Corner's Prize Exchange House can tell the player the type of Hidden Power their Pokémon has, and a man in the Battle Tower can judge the Individual values of the player Pokémon.
The price of the Accessories at Pick a Peck of Colors Flower Shop in Floaroma Town has been reduced.
European versions of the game are no longer able to play slot machines. These versions of the game replace slot machines with game machines, a machine that simply gives coins to the player with little interactivity. This is the result of changes in the classification standards at PEGI.[6]
As in Generations II and III, it is possible to ride a Bicycle in gatehouses separating cities or towns and routes, something that was not possible in Diamond and Pearl.
When the player uses their radar while in the Underground, it takes two seconds before another radar signal can be used. In Diamond and Pearl, it only took one second.
The Lustrous and Adamant Orbs are no longer found on the Spear Pillar as in Diamond and Pearl. Instead, they must be found in a cave somewhere in the snowfields of Mt. Coronet which requires Waterfall to access. To be able to catch Dialga and Palkia, the player must have obtained the items in that cave and must have faced Giratina, whether it was caught or not. The player can then go up Mt. Coronet to where Giratina took Cyrus into the Distortion World.
If the player defeats a stationary in-game event Pokémon (including most Legendary or Mythical Pokémon), it reappears next time the player enters the Hall of Fame. If the player defeats a roaming Pokémon, it will reappear only after the player has re-triggered the event which caused it to start roaming; for example, the player must talk to Professor Oak to cause a legendary bird to resume roaming. If the player flees from or defeats Origin Forme Giratina in the Distortion World, it will reappear in Turnback Cave in its Altered Forme, where it behaves in the same way as all other stationary Legendary Pokémon.
In Diamond and Pearl, this new rule applied to Dialga and Palkia only. In those games, entering the Hall of Fame causes them to respawn.
Most opponents' Pokémon's levels have been increased by at least one. An example of this is that in Diamond and Pearl, Barry's first partner Pokémon in the battle at Pastoria City is at level 28. In Platinum, it is at level 36. However, the Pokémon used by opponents in the Pokémon League had their levels lowered.
In locations where certain unevolved Pokémon can be found (like Numel on Route 227 and Stark Mountain), they are near the levels of the rest of the Pokémon in the area, whereas in Diamond and Pearl they were usually in the high 10s or low 20s.
All Gyms now only have Pokémon of their type specialty.

> Obtainable Pokémon
59 more Pokémon have been added to the Sinnoh Pokédex to give it a total of 210 entries, with all non-Legendary Pokémon introduced in Generation IV now included, along with their pre-evolved forms and several other Pokémon. The added Pokémon, such as Rotom and Giratina, are now available prior to the Pokémon League challenge.
Giratina has received a new Forme known as the Origin Forme, with its originally designed Forme retrospectively named the Altered Forme. Giratina will appear in Origin Forme while in the Distortion World, and Altered Forme outside. A Griseous Orb is required to transform it into its Origin Forme outside of the Distortion World.
The Ability of Origin Forme is Levitate and its base stats mirror those of Altered Forme, with the offensive stats switched with their respective defensive stats.
Shaymin's new Forme is called Sky Forme and takes on a canine appearance. Its Ability is Serene Grace, and the Forme is focused on Speed and Special Attack. It is able to learn new moves like Quick Attack, Air Slash, and Leaf Storm.
Shaymin can change between its two forms via the use of the Gracidea. Its Sky Forme will revert to Land Forme at night, if Shaymin is frozen, or when deposited into the PC.
Rotom has new forms as well. Each of the five forms is a Rotom that has possessed an electrical appliance. Despite having visual characteristics of other types, the five forms share the original Rotom's Electric and Ghost types; however, their base stats are significantly higher. They also share the original Rotom's Ability of Levitate. The item to unlock these Pokémon in the game, the Secret Key, is event-only. As these Pokémon are not normally available in this game, they were therefore banned from official tournaments[citation needed] until the release of HeartGold and SoulSilver which allowed Rotom to transform without the requirement of an event-only item.
Regirock, Regice and Registeel can be caught at level 30 with the help of an event Regigigas that has been distributed in Nintendo events.
Regigigas is now found at level 1, making it the lowest-level non-glitch wild Pokémon in any game along with Magikarp, as well as the lowest-level non-glitch Legendary in any game.
The legendary birds can be found as roaming Pokémon after the National Pokédex is obtained. They roam Sinnoh much like Mesprit and Cresselia do. The player has to talk to Professor Oak in Eterna City to trigger their appearance. They are all found at level 60.
Dialga and Palkia appear on the Spear Pillar one at a time after the player has spoken with Cynthia's grandmother in Celestic Town, and obtained the Adamant and Lustrous Orbs in Mt. Coronet.
Cynthia now gives the player a Pokémon Egg containing Togepi after the player has defeated Team Galactic at the Team Galactic Eterna Building, replacing the Happiny Egg previously obtainable in Hearthome City.
Bebe now gives the player an Eevee before the player receives the National Pokédex; Eevee can now be obtained from the first time the player arrives in Hearthome City. It is at level 20.
A man in Veilstone City gives the player a level 25 Porygon as a gift.
Manaphy, while still uncatchable in-game, is now required to obtain the National Pokédex. It can be added to the Sinnoh Pokédex from finding its picture in a book in the Pokémon Mansion.

> Missing Pokémon
These Pokémon are available in Diamond and Pearl but unavailable in Platinum. To be obtained, they must be traded from the other games of Generation IV or imported from a game from Generation III.
Misdreavus, Murkrow, Trapinch, Clamperl, Glameow, Stunky

[source][1]
[source][2]
(this answer doesn't include changes to glitches, and it also doesn't include a full list of individual movepool changes. please comment on the answer if you want these included or if it's missing something else)


  [1]: https://bulbapedia.bulbagarden.net/wiki/Pok%C3%A9mon_Platinum_Version
  [2]: https://bulbapedia.bulbagarden.net/wiki/Pok%C3%A9mon_HeartGold_and_SoulSilver_Versions

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> Areas
Much like Pokémon Emerald, a new Battle Frontier takes the place of the Battle Park. It has the Battle Tower, Battle Factory, Battle Castle, Battle Arcade, and Battle Hall as venues.
Twinleaf Town and nearby routes now have snow patches.
This provide evidence that this version may take place in winter, as opposed to the previous Sinnoh installments which do not have a definite season.
Jubilife City has been refurbished with new pathways and some buildings have animated roof lights.
The Global Trade Station in Jubilife City has been redesigned and now includes a bigger global terminal. It has been renamed as the Global Terminal.
Oreburgh Mine now has twin coal transporters starting from the entrance and ending at the entrance to the last section of the mine and move.
An arch now represents the entrances to Floaroma Town.
The trees in the Eterna Forest, as well as Fullmoon Island and Newmoon Island, cast shadows that cover the ground.
Eterna City has been refurbished with new foliage and pathways. Also, the Team Galactic Eterna Building has had a complete redesign, inside and out. It now contains a secret room where Rotom can switch between its forms.
Cycling Road has been redesigned and now has tunnel-like shelters in the middle of the Cycle Route, as well as lights along the sides of it.
Hearthome City has been refurbished with new pathways, and the gates leading to Amity Square have a new design with signs that light up at night.
Amity Square has been completely remodeled. It now includes a small pond, more paths, and more upper levels. The old buildings that previously inhabited Amity Square now contain Warp Panels which transport the player to the other old buildings within Amity Square.
Lost Tower has had its color scheme changed and now has fog on three of its five floors, which can be cleared by HM05 (Defog).
Solaceon Town's houses have been remodeled and the Pokémon Day Care now has a trough filled with water and tent-like shelters.
Veilstone City has been refurbished with new pathways. The Galactic Veilstone Building has been redesigned, inside and out. The Veilstone Department Store now has a basement, in which Poffins can be sold and bought. Berries and Lava Cookies can be bought as well.
The Hotel Grand Lake has been refurbished with new pathways.
Pastoria City's houses have been remodeled, and now also includes a board with a Croagunk on it, which is located in front of the Great Marsh. Occasionally, if the player stands behind the Croagunk Wall with the player's head sticking out of it, a wild Croagunk will come, but it will just cry and walk into the Great Marsh building.
The Great Marsh has had its color scheme changed, and has also had foliage changed and added.
Celestic Town's houses have been remodeled.
Canalave City has been refurbished with new pathways, and its houses and library have also been remodeled.
The player now needs to use HM08 (Rock Climb) to reach Lake Acuity.
The area of water to the south of Snowpoint City, where the player can get a boat to the Battle Zone, now contains a small number of icebergs. These can also be seen in the ocean when the boat is crossing to the Battle Zone. The boat has also been redesigned, most likely due to the icebergs in the sea.
The back area of Spear Pillar has been slightly redesigned to allow more room for the Pokémon of myth when they appear.
Sunyshore City has been refurbished with new pathways, and its houses have been remodeled.
The entrance and exit of Victory Road have become wider, having a Poké Ball at the center of the arch.
The Battle Zone is now warmer, and palm trees can be found there.
Stark Mountain now has more features evocative of a volcano, such as crags and pits of lava.
The Pokémon Mansion is surrounded by golden railings.

> Storyline
The story seen on TV at the start of the game is now about Professor Rowan having just returned from a trip to Kanto.
The player meets Professor Rowan and the opposite gender character earlier, and obtains their first partner Pokémon on Route 201.
Instead of being attacked by wild Pokémon at Verity Lakefront, the player and their rival are attempting to reach Sandgem Town through tall grass when the Professor stops them, and offers them a first partner Pokémon.
The first battle is against the player's rival, who has chosen the first partner Pokémon which has a type advantage against the player's.
The player and the rival now encounter Cyrus at Lake Verity at the start of the game. The player can also meet Cyrus at different venues such as the Eterna City statue.
Both Dialga and Palkia appear on the Spear Pillar. Giratina, the mascot of Platinum, then phases into the world in front of Cyrus.
A new area known as the Distortion World is playable. It has floor-like sections floating at ninety-degree angles from each other, creating an effect similar to the art of M. C. Escher. It disobeys the laws of physics, making things like Surfing down a waterfall going up possible. The camera angle switches between perspective and isometric views to suit the angle of the player. It also has moving platforms with jumpable gaps between them. Giratina, when here, will be in its Origin Forme, and is also the only wild Pokémon located here.
Two new characters to the main storyline were added. One is Charon, a professor and Commander of Team Galactic, and the other is a police officer spying on Team Galactic, using the codename "Looker".
A Tag Battle between the player and their rival against Flint and Volkner takes place at the entrance to the Battle Frontier when the player first arrives there.
Team Galactic's plans to re-create the world has changed slightly. The layouts of their HQs, such as the one in Eterna, have been changed. Team Galactic now utilizes more resources to reach their goal, as well as explaining why, in-game, such as the power from the Valley Windworks, as well as planting a bomb on the Great Marsh for attention to allow more people to realize what they're trying to do. Team Galactic also has a fourth commander who appears throughout the game, but does not take on a significant role until after the main story events.
Some of the Gym Leaders have been reordered: Fantina is now the third Gym Leader; Maylene is the fourth; and Crasher Wake is the fifth. The appearance of players' Gym Badge case stays the same.
Dawn/Lucas now gives the player the Dowsing Machine or the Vs. Seeker at the entrance to Mt. Coronet, instead of near the Route 206 junction.
Team Galactic appears in Stark Mountain under the command of Charon, who seeks to use the destructive power of the volcano to extort money from the people of Sinnoh. The player, with help from Buck, must defeat them. During this event, Mars and Jupiter quit Team Galactic because Charon does not share the same ideals as ex-boss Cyrus. Ultimately, Charon and his two accompanying grunts are apprehended by Looker and two policemen.
After the aforementioned event, the player can challenge all the Gym Leaders of Sinnoh to rematches in the Battleground. The player's Tag Battle partners from throughout the game (Cheryl, Buck, Marley, Mira, and Riley) are also able to be challenged in this place. Each of the 13 characters has a team of five Pokémon, whose levels are between 61 and 65 (except for Maylene, whose team instead ranges from level 62 to 66).
The Pokémon League increase their Pokémon's levels after the player has completed the Stark Mountain event. Their levels are now between 65 and 78.
When one finishes the Stark Mountain quest, instead of the rival appearing at the Fight Area on weekends, he now appears at the Survival Area in front of the Battleground. During the first battle, the levels of the Pokémon in his party range from 59 to 65; in the second battle, from 69 to 75; and third and beyond, from 79 to 85. In these last battles, he was the Trainer with the highest-leveled Pokémon in all core series games, until Red's remade team in Pokémon HeartGold and SoulSilver.
When first visiting the Resort Area, the player is offered a Villa. If they accept the offer, items can then be purchased to furnish the house in the same manner as decorating a secret base. The player will be visited by NPCs such as the Sinnoh Gym Leaders, the player's mother, Professor Rowan, and the rival.

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> Graphics
Lucas, Dawn, and Barry have different outfits designed for colder weather, as the entire Sinnoh region has changed in temperature.
The template for the level, HP, and the name of Pokémon in battle is a dark gray instead of white, and its shape has changed.
The Pokétch has been redesigned. Players can now move up and down between apps instead of having to go through all of them to return to a previous one.
Some of the moves have been redesigned, and have a different animation, such as Razor Leaf and Spacial Rend.
When Pokémon are sent out from their Poké Balls, their back sprites now animate much like their front sprites have since Emerald (i.e., multiple frames of animation in addition to the various distortions and filters already used).
Some back sprites, while mostly similar to those of Pokémon Diamond and Pearl, experience several minor stylistic changes, such as size changes, correction of graphical errors, pixel enhancement, and changes in color tones. A few Pokémon have very noticeable changes, such as Azumarill and Gligar, among others.
Front sprites for Generation IV Pokémon and other Pokémon in the Sinnoh Pokédex have also changed. Meowth, Muk, Oddish, Hitmonlee, Ninetales, and Primeape also receive new sprites despite not being in the expanded Sinnoh Pokédex, while Registeel uses its sprite from the German, Italian, Spanish, and French versions of Diamond and Pearl. The Diamond and Pearl sprites are still used when the player dresses up the Pokémon either in Super Contests or in the Jubilife TV station.
When battling certain Trainers such as Gym Leaders, Frontier Brains, and Barry, the Trainers' sprites are now animated to move in the same manner as Pokémon.
Some Trainers now use Seals when sending out some of their Pokémon.
The Eterna, Hearthome, and Veilstone Gyms have all had complete redesigns in the interior.
Closeups of Gym Leaders, just before a battle, have been changed from enlarged sprites to higher-quality drawings, and the term "VS" has been added; the Frontier Brains also have this feature. The Elite Four have this as well, but the animation includes the player on the left side of the "VS." and the Elite Four member on the right side.
The rooms where the player battle the Elite Four have been redesigned. Aaron's room now has logs and foliage; Bertha's now has rocks; Flint's now has lava pits; Lucian's now includes four large glowing orbs on the floor; Cynthia's room has changed its color scheme, and the lift leading up to the Hall of Fame is now partially contained. The Elite Four and Cynthia now all have unique battle backgrounds. The Pokémon Center at the Pokémon League has also been redesigned.
When entering new areas, the location "labels" on the top-left corner have been redesigned, much like they were between Pokémon Ruby and Sapphire and Pokémon Emerald.
Pikachu and Pachirisu are now featured when entering Wi-Fi.
The Pal Pad has been given a new design.
The game director at Hotel Grand Lake now has an overhead sprite of his own. The Diploma also was redesigned.
When the player starts the battle with the Giratina in the Distortion World, instead of displaying "A wild Giratina appeared!", it displays "The Distortion World's Giratina appeared!". It is referred to as "the wild Giratina" in other instances, such as attacking, however.
The trees in West Sinnoh have sharper angles and a point at the top, compared to rounded branches and a rounded top in Diamond and Pearl, and are also slightly darker. The trees in East Sinnoh are also slightly darker, but are now a completely different hue than the trees in West Sinnoh, and are more rounded than in Diamond and Pearl, while the Battle Zone has completely new trees altogether.

> Sound
Giratina's cry will be heard when "Start" or "A" are pressed at the title screen, unlike in Pokémon Diamond and Pearl, which just play a snippet of the title theme's melody. It shares this trait with some other games.
The Mystery Gift theme has changed to a more upbeat version of the theme used in Pokémon Diamond and Pearl.
The Battle Tower theme was changed slightly to have more guitar-sounding riffs and more dynamic transitions.

Pt to HGSS

> Gameplay
All 493 Pokémon are capable of following players similar to Pikachu in Pokémon Yellow. Shininess and form differences are retained when a Pokémon is following the player. The player can interact with their Pokémon by pressing 'A' while facing it, so they can see how their Pokémon is feeling at the moment. In battle, like Yellow's Pikachu, they are sent out from the side of the screen, rather than from a Poké Ball. The player's lead Pokémon will always follow them except in certain situations, such as while riding the bicycle, surfing, or going indoors with a large Pokémon.
Kurt and Apricorns make a return to the series along with the respective Poké Balls. Apricorns are now carried by the player in a new item, the Apricorn Box. As in Crystal, Kurt can be given multiples of the same color Apricorn at once in order to make multiple Poké Balls.
Similar to the event Shaymin and Regigigas in Platinum, two in-game events are unlocked through the use of event-exclusive Pokémon. The Pikachu-colored Pichu unlocks an event near the Ilex Forest shrine where the Spiky-eared Pichu can be obtained, and an event-exclusive Celebi unlocks an encounter with former Team Rocket boss and Viridian Gym Leader Giovanni. Giovanni was mentioned repeatedly in the original Generation II games but did not appear. These events effectively replace the GS Ball event formerly found in the Japanese version of Pokémon Crystal.
The Pokémon Storage System, Bag, party interface, and the screen that pops up when pressing the Start or X buttons in the previous games all use the Nintendo DS's touch screen.
Cynthia makes an appearance in an event involving Arceus. This takes place in an area accessed from the Ruins of Alph that is far to the north, named the Sinjoh Ruins. This event allows players to obtain either Dialga, Palkia, or Giratina at level 1. The only way to obtain the Griseous Orb and Origin Forme Giratina in this game is to choose Giratina during this event.
Apricorns are now the only items collected from plants on the field. Berries are instead collected from Jugglers in Violet City and Fuchsia City in exchange for shards, through the Pokéwalker's Dowsing function, hidden on the ground, or from the deliveryman in Poké Marts sent by the player's mom (if the player allows their mom to save money). A few Berries cannot be collected in these games and must be traded over from other versions, similar to in FireRed and LeafGreen. Though they cannot be grown on the ground like in Hoenn or Sinnoh, they can be grown portably using the Berry Pots, where the SquirtBottle is controlled via the touch screen to water four Berries at a time.
The Running Shoes are obtained in Cherrygrove City and can be permanently selected using the touchscreen menu. The selected item (from pressing Y or SELECT in previous games) is also on the touchscreen. Two items can be selected as opposed to just one.
When the player is choosing their first partner Pokémon (Chikorita, Cyndaquil, or Totodile), it is possible to check if any of them is Shiny before obtaining them.
Many Pokémon have acquired the ability to learn new moves and expand and improve their movesets; for example, Togepi can now learn Extrasensory through breeding.
An addition to the breeding system is introduced where one of the three random IVs inherited by the offspring can be guaranteed if one of the parents holds a Power item.
The player doesn't need to encounter the roaming legendaries before being able to track them on the map.

> Graphics
Much like Kanto's was for its remakes, Johto's Pokédex has been redesigned. Unlike Kanto's remakes, which contained the same regional Pokédex as the originals, the original regional Pokédex for Johto has been slightly altered, including five Generation IV Evolutions for Pokémon found in Johto.
If the player turns off the battle scene in the Options menu, the Pokémon will not be animated when they come into battle, whereas in Platinum they were.
When viewing the stats of a Pokémon outside of battle, one of the stat names will be very light blue, indicating which stat is decreased by the Pokémon's Nature, and one will be very light red, indicating which stat is increased. If the Pokémon has a neutral Nature, none of the stats will be colored.

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This is a lot of good info! This is all stuff I pretty well already knew though, these are pretty standard inter-game differences. My original questions (and attached comments) were more specifically aimed at things like levelup move sets, rebalanced moves and stats, more fundamental changes to the game, like the kind you'd usually see between generations. Stuff like different graphics or mechanics, new move tutors, etc. are all pretty standard, and as your sources show, really easy to find on the game's wiki pages. I'm looking more for niche changes that the average person might miss, like what Froggyfrogsock mentioned about Hypnosis having a different accuracy in DP. Looking for the really obscure and minute changes that were made mid-generation instead of after like usual.

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All of those changes should be documented somewhere on Bulbapedia. It's going to take a long time for anyone to compile them into one answer, though.

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Niche changes that the average person might miss is a very broad category. So are changes you'd usually see between generations.
I know you're doing your best to give examples but it would help a lot if you just said, give me a list of occasions where specifically x y or z happened.

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I think most of those changes would be level up moves. As far as I know, hypnosis, thunder, and blizzard are the only moves that had their effects changed.