Mew is so cute, yet so strong. If anda looked at it without knowing anything about pokemon, anda would assume it was weak... then it would kick your ass. XP Unexpected power - I always find that sort of thing cool! So that's my reason. X3
It's very rare and legendary! It learns LOTS of moves but not exactly ALL of them, What about Diamond Storm? Only Diancie/Mega Diancie knows that. It's also adorable :3