Norskak Executioner

When Norskak Executioner enters the battlefield, put a doom counter on target creature an opponent controls. The counter remains on that creature until either Norskak Executioner or the creature it targets leaves the battlefield.
Whenever Norskak Executioner blocks or becomes blocked by a creature with a doom counter on it, Norskak Executioner gets +2/+0 and gains first strike until end of turn.