Does Carracosta's "Ancient Custom" Ability negate Stealthy Hood? Or does Stealthy Hood prevent "Ancient Custom" from affecting the Pokemon Stealthy Hood is attached to?
Stealthy Hood prevents Ancient Custom's effect on the Pokemon Stealthy Hood is attached to.
Source: TPCi Rules Team (2020-03-12)

Relevant cards

Note: All applicable cards may not be listed below.
SM10_186
SM10_186
SM11_45
SM11_45