mtg wolverine card Magic the Gathering Secret Lair x Marvel's put a +1/+1 counter on him Wolverine, Best There Is -

Secret Lair is Magic: The Gathering's self acclaimed "best worst-kept secret"

A 2-drop creature that exiles everything your opponents play is potent enough without the ability to cast one of them for free

That was Darksteel

One token every upkeep adds up quickly

Other possibilities include instants and sorceries that have a kicker effect tied to dice or artifacts that allow you to roll dice and gain benefits

This ability is eminently impactful both offensively and defensively, as it can be activated before combat to make your creature unblockable by a specific color, or it can be activated in response to one of your creatures being targeted by a specifically colored spell to make it invulnerable