Etali, Primal Storm

Whenever Etali attacks, exile the top card of each player's library, then you may cast any number of spells from among those cards without paying their mana costs.

Nathan Drake, Treasure Hunter

First strike
You may spend mana as though it were mana of any color to cast spells you don't own or to activate abilities of permanents you control but don't own.
Whenever Nathan Drake attacks, exile the top card of each player's library. You may cast a spell from among those cards.

Passionate Archaeologist

Commander creatures you own have "Whenever you cast a spell from exile, this creature deals damage equal to that spell's mana value to target opponent."