Search your deck for a card that evolves from Feebas and put it on Feebas. (This counts as evolving Feebas.) Shuffle your deck afterward.
This card's Ascension attack was later errata'd so that a successful coin flip of heads was necessary to activate the effect. The errata was listed to only affect Feebas; the ruling also mentioned the set's Vulpix card did not need a coin flip for its Ascension attack.