>>49808574Trade evolutions were a thing because the trading process has imperfections and it sometimes causes the two Pokemon to fuse. For instance, Graveler loses two arms when it evolves, while Machoke gains two arms. Kababra become significantly lighter when it evolves, while Haunter becomes much heavier. It's also why Bill's teleportation experiment (a precursor to trading) went wrong and he got fused with a Pokemon.
These evolution methods are a way to flesh out the lore in Pokemon games, only brainlets dislike them.
