Porygon2

Porygon2 is a solid Trick Room supporter because its incredible bulk, lack of many weaknesses, and access to Recover make it very difficult to brute force down for the KO. It takes little damage from most attackers, avoiding 2HKOs from even the heaviest hitters in the metagame such as Mega Charizard Y, and it is able to Recover its HP against weaker attackers. Notably, Porygon2 is one of the rare Trick Room setters without a weakness to Dark- and Ghost-type attacks, letting it set up Trick Room in the face of Pokemon such as Hydreigon and Aegislash, which otherwise trouble Trick Room setters.

However, Porygon2 is reliant on Eviolite for its bulk, meaning it is weak to Knock Off and cannot use any other items such as Safety Goggles. As a result, Taunt and Spore completely nullify Porygon2's presence and deny its attempts at setting up Trick Room. Porygon2 also lacks relevant resistances and needs to stay at high HP to be effective, so it needs to use Recover more often than not. This, combined with its mediocre offenses, turns Porygon2 to a huge momentum sink and in turn opens up the opponent to simply ignore Porygon2 and set up or gang up on its partner.