Why does Mewtwo outdamage Gengar vs Cresselia?
Cresselia is a pure psychic type, just like Mewtwo is. So why did legacy Gengar top the charts on DPS against Mewtwo (with SB Mewtwo a close second), but Mewtwo tops the charts against Cresselia with Gengar a distant second? There's over a 1.5 DPS gap between them, Mewtwo does more than 10% more DPS than Gengar against Cresselia according to the guide here?
Answers
The guide here is comparing Hex gengar to Mewtwo, not Shadow claw or Lick gengar, that's why. If you hover over gengar's icon in the rain graph, it says 'non-shadow claw gengar'.
Lick/Shadow claw gengar still beat Mewtwo.
It's possible that against some things, gengar will lose out even with shadow claw. This is because it's so squishy that it's more likely to die with wasted energy earlier than mewtwo - this can have a big effect on dps. But that's not the case vs cresselia