Xendra, Fate Shredder

Doom 3 (Whenever this creature deals damage to a player, choose one; put a doom counter on this creature, or remove 3 doom counters from this creature. For each doom counter removed this way, that player puts the top 3 cards of their library into their graveyard.)
{1}{u} : Xendra can't be blocked this turn.
{1}{b} : Regenerate Xendra.