Tyranitar is a Rock/Dark type Pokémon that is strong against Bug, Fire, Flying, Ice, Psychic, and Ghost-type Pokémon. However, it is weak against Fighting, Bug, Fairy, Grass, Ground, Steel, and Water-type Pokémon. Therefore, the best counters to Tyranitar in Pokemon Go are Fighting, Bug, Fairy, Grass, Ground, Steel, and Water-type Pokémon. Some of the best options include Mega Blaziken, Terrakion, Shadow Machamp, Keldeo, Shadow Hariyama, Conkeldurr, and Polywrath. It is also worth noting that one high-level trainer can beat Tyranitar with weather-boosted Fighting type counters, but otherwise, 2-3 trainers will suffice.