Veldrane, Sengir's Tracker

Swampwalk, forestwalk
Whenever Veldrane, Sengir's Tracker deals
combat damage to a player, that player
reveals cards from the top of their library until
they reveal a creature card. Exile that card. You
may cast that card for as long as it remains exiled,
and you may spend mana as though it were mana
of any type to cast that spell. Then that player
puts the rest of the cards revealed this way into
their graveyard.