>>50307493I've thought about this a little. The only way it really could work is as Sub-Types. Pokemon always have 1 or 2 Types and 0-1 Sub-Type. The Sub-Type IN NO WAY effects the battle weaknesses and resistances of the Pokemon. That's the only way it can reasonably work.
I'm unsure what Sub-Types would actually do but they're essentially an extra affinity for a Type. Easy example would be that STs determine what Hidden Power you have. STs are non-permanent, you can change them freely with NPC training or using items or something, into any Sub-Type you want, and most wild Pokemon do not have any ST by default when caught.
However, certain Pokemon species all have a certain Sub-Type in the wild. All Salazzle have Dark as an ST when you first catch them, all Flygon have Bug, all Malamar have Water, all Gourgeist have Fire, etc. It's a way to SUGGEST these Pokemon have 3 Types without completely fucking over game balance and overcomplicating it. Sort of like recessive genes.
In these instances where Sub-Types can be found naturally on all members of that species, the Sub-Type will provide very slight STAB bonus to moves of that Type, probably not more than 1.2x. Maaaaaaybe also very very slight resistance to that Type's attacks, not sure.
Inputs to give?
