Quoted By:
>Evolution by trade. According to your imagination, how exactly does it work?
Well, ya see....
You train your Pokemon, level them up, make them stronger, and they bond with you. Like it or not, your Pokemon looks up to you, like parent or an older brother. You may not bond with them though, after all, they're just another dex entry, right?
By the time your Pokemon realizes you don't feel the same way though, it's too late. It's poor naive little mind could not comprehend the fact that you just don't love it, and you were so willing to give it away to another trainer.
Overcome with sadness and fueled by anger towards its ex-trainer the Pokemon unlocks strength that no-one knew it had inside it. With the sheer force of hatred they feel towards you their old form simply cannot contain it. So it evolves.
With its new body and abilities it vows to become the strongest, fastest and best it possibly can. Just so it can defeat you. Make sure you feel the same way you made it feel. An eye for an eye, right?
...... and that's why Pokemon evolve when you trade them.
How do you spell "edgy"?
