Krev and Sab, Scheming Killers

When this creature enters the battlefield put a
-1/-1 counter on target creature, then Krev and Sab, Scheming Killers fights that creature.
When this creature fights another creature it gets
+1/+1 for each -1/-1 counter on that creature until
the end of the turn.
{2}{t}: Fight target creature an opponent controls.