Serin Darkhound

Mutate {1}{b/r} (You may play this card for its Mutate
cost, and when you do, place it on over or under a
Creature card. The card on top has the abilities and effects of the card underneath.)
Stealth, Venom Bite (Whenever this card deals
damage to a Being or Creature card, place a -1/-1
counter on that card.)
When this card mutates, deal 3 damage to the opponent's Vitality.