Fenrir, Vengeance Unchained

First strike
As long as Fenrir, Vengeance Unchained is
blocked, it has deathtouch.
Whenever Fenrir deals combat damage to an opponent, place one Bleed counter on it. Fenrir
gets +1/+0 for each Bleed counter on it. During
your upkeep, if there are four or more Bleed
counters on Fenrir, you may have Fenrir deal
damage equal to its power to target creature. If
you do, remove all Bleed counters from Fenrir.