Riven, of a Thousand Voices

Lifelink, Trample
Whenever a player pays life to cast a spell or activate
an ability, Make a Wish. (To make a wish, put the
top 3 cards of your library face down. Target
opponent exiles one with a Wish Counter. Shuffle
the other 2 into your library.)
Whenever Riven, of a Thousand Voices Enters or Attacks, you may cast a spell in exile with a Wish
Counter without paying its mana cost.