Kostas, the Wayfarer

Prowl {u}{b} (You may cast this for its prowl cost if
you dealt combat damage to a player this turn with a
Rat or Rogue.)
Whenever another Rogue enters the battlefield
under your control, if you paid it's prowl cost,
Kostas, the Wayfarer explores.
Kostas has skulk as long as it has at least one
+1/+1 counter on it.