Change is Bad
The Metagame: unchanged since 1899.
Metagame premise: Suppose Game Freak never updated anything but rather only made new stuff? That's this meta idea. Things function as they were introduced. Basically...
-All Pokemon have the typing and BST they were introduced with. For example, Magnemite and Magneton are Electric types, but Magnezone is still Electric/Steel. Gardevoir is a Psychic type but Mega-Gardevoir is a Psychic/Fairy.
-All Gen 1 Pokemon have Special Attack and Special Defense equal to their Special stat. Megas, however, have the stats they were introduced to, which could lead to some stat drops.
-All moves have the same typing, base power, PP, and secondary effects they were introduced with, including any bugs. For example, Leech Seed stacks with Toxic, Low Kick is BP 50 with a 30% flinch chance, Wrap prevents either side from taking action, etc.
-All abilities function as they were introduced. For example, Sturdy no longer prevents OHKOs from non-OHKO moves and Lightning Rod no longer grants Electric immunity nor grants a Special Attack boost.
-All status effects function as they were introduced. For example, sleep lasts 1-7 turns, resets on switching, and the Pokemon takes no action on waking. Frozen Pokemon never thaw unless using or being hit by moves that cause it.
-The type chart functions as the types were introduced, with later added typings taking precedence. For example, Bug and Poison are super-effective against each other, Steel resists Ghost and Dark, but Psychic is still weak to Dark and Dark is still weak to Fairy. Additionally, Grass-types are no longer immune to powder moves, Electric types immune to paralysis, etc.
-All items function as introduced. Sitrus Berry only restores 30 HP rather than 25%, for example.
Notable exceptions: All Pokemon have access to their modern move and ability pools. This is to keep older Pokemon from getting shafted hard by having old, crappy movepools or Gen I and II Pokemon from having no abilities, III and IV not having hidden abilities, etc while everything Gen V and later would more or less laugh at everything.
I'm not coming up with a full list of differences here since that'd be a lot of work. It'd be something I'd save for if it was accepted.
Potential bans and threats: -Freeze clause would be implemented due to Pokemon not thawing on their own
-Wrap, Bind, and Fire Spin would be banned since fast Pokemon would be untouchable by slow
-Wobbufet, because two Leftovers Wobbus would get stuck in an endless loop due to Shadow Tag and Struggle doing less damage than Leftovers recovery
-Sky Drop, because it'd be bugged again like Gen V.
-Soul Dew because old Soul Dew was always banned for a reason.
-I'm sure I've missed some...
It's hard to predict threats with how much things would change. But I can see like Chansey becoming threatening since it'd now have a 105 Special Attack.
Questions for the community: -Did I miss anything major?
-Should I blend old movepools into new ones? Aka, if a Pokemon ever learned a move in any generation, it can learn it in Change is Bad. Such as Charmander learning Metal Claw in FRLG, so it'd be legal on any Charizard set. Go go Teleport Arcanine! Or should it be strictly modern movepools?