Shedinja

Shedinja has an amazing ability in Wonder Guard that leaves it immune to anything it isn't weak to, giving it loads of switch-in opportunities against some very threatening Pokemon such as Samurott, Kangaskhan, Klinklang, and Ludicolo. It also has a decent Attack stat backed by STAB priority in Shadow Sneak to somewhat make up for its lack of Speed. Thanks to Wonder Guard, Shedinja forces a lot of switches because many foes don't carry coverage moves to hit it with, rendering them helpless. Unfortunately, not only does Shedinja have a number of common weaknesses and a pathetic 1 HP that can't even be invested in, but it is also weak to all entry hazards, meaning that it cannot even switch in if they're on the field. Moreover, Shedinja is extremely vulnerable to being pursuit trapped by Pokemon like Skuntank and Liepard, making it a liability in certain matchups. Therefore, in order for Shedinja to be effective, it needs support in the form of Pokemon that resist its weaknesses, status absorbers, and hazard control in some from, whether that be Magic Bounce, Rapid Spin, Defog, or any combination of the three.