Question: what happens after you catch mewtwo pokemon let's go?
Answer: Once you've defeated Mewtwo in battle, it's time to catch it! Now, you could spend a lot of time, Razz Berries, and Ultra Balls to add this Legendary Pokémon to your party, but this is a prime opportunity to use your Master Ball, if you still have it, which will catch any Pokémon without fail.