[PKM] Undersea Ruins (138/147) [Aquapolis]

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

Once during each player's turn (before attacking), that player may flip a coin. If heads, that player chooses 1 of his or her Evolved Pokémon in play and discards the top Evolution card from that Pokémon, devolving it.