* Bug
* Ghost
* Dark
So, Pokemon with these types will be super effective against Mewtwo.
Here are some examples of Pokemon effective against Mewtwo:
Bug-type:
* Scizor (Steel/Bug)
* Pinsir (Bug)
* Heracross (Bug/Fighting)
* Genesect (Bug/Steel)
Ghost-type:
* Gengar (Ghost/Poison)
* Chandelure (Ghost/Fire)
* Aegislash (Steel/Ghost)
* Mimikyu (Ghost/Fairy)
Dark-type:
* Weavile (Dark/Ice)
* Hydreigon (Dark/Dragon)
* Tyranitar (Rock/Dark)
* Houndoom (Dark/Fire)
However, keep in mind that Mewtwo has high Special Attack, so Pokemon with high Special Defense are also recommended.
Remember, this is just a starting point. There are many other effective Pokemon out there, and the best choice will depend on your specific team and strategy!