What to check
The Legendary bird requirement is to catch all three. Defeating them or completing their challenges does not by itself satisfy the capture requirement.
PokéBonk — How do I unlock Mewtwo?
The short answer
Mewtwo's League challenge requires all of the following:
- Have 60 members in your League.
- Catch Articuno, Zapdos and Moltres.
- Clear Pewter Desert twice on Hard difficulty.
