Quoted By:
>I have no idea how tiers work
Tiers are based on usage. He's PU because people don't use him.
While he's viable in pretty much all tiers, his only real role is a revenge killer with a scarf, and while having a Boosted Mega Scarf'd mon can be great, you're locked into one move, and often can be easily countered. There's also the fact that if the opponent doesn't really have a dedicated sweeper, Ditto can't do much. There's also the fact that thanks to his pitiful HP, he can be often beaten by the things he's meant to revenge kill.
