As this artifact enters, choose a creature type.
Whenever you cast a spell of the chosen type, put a charge counter on this artifact.
Creatures you control of the chosen type get +1/+1 for each charge counter on this artifact.

Prowl (You may cast this for its prowl cost if you dealt combat damage to a player this turn with a Goblin or Rogue.)
When this creature enters, if its prowl cost was paid, search target opponent's library for three cards and exile them. Then that player shuffles.