Seleneas, the Planar Posion

Skulk, hexproof, deathtouch
Whenever Seleneas attacks, you may pay
{u/b}{u/b}{u/b}. If you do, choose a creature the defending Player controls. Tap that creature. When Seleneas deals combat damage to the defending Player, destroy the chosen creature at the beginning of the next untap step.
{u}{b}: Exile Seleneas, then return him to the battlefield. Target opponent loses 2 life.