Mirage Stadium (Skyridge 132/144)

Rules

This card stays in play when you play it. Discard this card if another Stadium card comes into play.

Whenever a player tries to retreat a Pokémon during his or her turn, that player flips a coin. If heads, that player retreats that Pokémon (and discards Energy normally). If tails, that Pokémon can't retreat this turn (the player doesn't discard any Energy).