Unown is randomly assigned a letter when encountered.
Shellos and Gastrodon are west sea if found in western Sinnoh, Kalos, or Hoenn and east sea if found in eastern Sinnoh or Alola.
Deerling and Sawsbuck change sprite along with the season in Generation 5 and never change in later games. In later games, they're always spring form unless transferred from a Generation 5 game.
Keldeo is resolute form when it knows secret sword.
Vivillon's sprite depends on the real-world location where the player's 3DS was from.
Flabebe, Floette, and Florges have different colors depending on the color of the flower that they came from.
Furfrou changes sprite when groomed.
Xerneas changes to active mode when entering battle.
Mimikyu becomes busted when disguise activates.
Solgaleo and Lunala change to radiant sun form or full moon form when using their signature moves.
Alternate forms of Pichu were obtainable in events in HGSS.