There are a lot of formats that are in the teambuilder but not in Smogon's Strategy Dex, but they all fall into these categories.
Old Gens
These formats use game mechanics from older generations.
Ruins of Alph subforum
Other Metagames
An OM is any Smogon metagame that isn't officially recognized by Smogon (this does not include pet mods). They don't have top-level subforums or official Tier Leaders. OMs typically make broad changes off a consistent rule, or small set of rules. For example, introducing a new mechanic (Pokemon have the type(s) of their first two moves - Camomons) or providing access (Pokemon can use any ability - Almost Any Ability). Cartridge-playable OMs don't alter mechanics but either restrict (only Pokemon that can evolve are allowed - NFE) or unrestrict (anything that can be hacked is allowed - BH). Pokemon that become extremely powerful if allowed to have new elements are not granted special accommodation to remain legal by virtue of being exempted from the OM's rules. (i.e. AAA doesn't keep Shedinja legal while denying it the core gimmick of the meta - it just bans the Pokemon). In short, an OM can usually be summarized accurately and completely in a sentence or two.
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list of OMs
Pet Mods
This is the place to contribute to Pet Mods, which are similar to Other Metagames in how they change how you play the game. The big difference is that Other Metagames have one rule applied to the whole game without changing any specific mechanics, like "every Pokemon gets every move of its type," while Pet Mods have more specific changes, like giving a bunch of Pokemon new and unique abilities that don't exist in the main series. Pet Mods also tend to be way more community-centered than Other Metagames, with anyone being able to submit changes or additions to a Pet Mod.
There's also a group of Pet Mods called Solomods. There are some specific ideas that don't quite fit as Other Metagames or Pet Mods, like where in-game mechanics need to be changed to fit the "one rule" Other Metagames typically need or having specific changes like Pet Mods without the community focus. That would typically describe what a Solomod is. If you're ever unsure of what your idea may be counted as, you're free to post about it in the Workshop or message one of the staff!
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Draft Leagues
A draft league is where individuals (coaches) take turns drafting teams of unique Pokémon and battling each other weekly until one coach is crowned the Champion. They do this by analyzing how their 8-12 Pokémon match up against their opponents' and then bringing the best six of their draft to counter their opponent's draft. Many servers center their identity and niche around the members of their community and those members' connections to the draft league community as a whole. Whether your desire is to be the best draft league coach on the scene, try out any number of custom metas, or experience what it's like to run your own community, the draft league community will grant your wish and more. Being able to realize nostalgic interest in Pokémon with a group of friends across the globe, sharing and creating new memories together, is an amazing thing. Any acronym you may see mentioned in this article may be found at the very bottom under the category titled "VI. Legend".
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Draft League subforum
Metronome Battles
This has been a thing since back in the Shoddy Battle days, where people would use Pokemon with the move metronome to battle and pray the RNG is on their side, so let's bring that back with some small twists here and there.
Keep in mind that this is a 2 vs. 2 format.
So yes, the only thing you need to do is use metronome in battle. That's it.
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One last thing that's worth mentioning is custom game, which is not listed in the teambuilder. You can challenge another user and then select any team to bring to the battle.
Allows anything within the capabilities of PS, which includes levels up to 9999, at most 24 moves each, illegal moves and/or abilities. The "New Box" feature in the teambuilder also allows you to use up to 24 Pokémon in this mode as well.
source: entering "/rfaq customgame" in Showdown!'s help room
