>>21369184I've been thinking about it, and it could work if it were not a broken or nonsensical method.
I'd like it to be an in-battle only thing like Mega Evolution, but that would mean it would only be possible in Doubles/Triples where there can be multiple Pokémon to fuse. If it were possible outside of battle, non-fused Pokémon would probably be shyed away for more powerful fused counterparts.
Another matter is if it is a permanent fusion or not; which it really shouldn't be.
The last real issue is which Pokemon can fuse. The way I have it figured is that they'd have to be a set compatability list, based around body shape, size, and both units being the same gender, to avoid silly gender swapping controversy.
Stuff like Lucario/Zoroark, Milotic/Serperior, Aggron/Tyranitar, Steelix/Gyarados; but not stuff like Pikachu/Arceus.
So yeah, theoretically it could work, so long as the right decisions are made as to how it's implemented.