Kotis, the Fangkeeper

Indestructible
Whenever Kotis deals combat damage to a player, exile the top X cards of their library, where X is the amount of damage dealt. You may cast any number of spells with mana value X or less from among them without paying their mana costs.

Gonti, Canny Acquisitor

Spells you cast but don't own cost {1} less to cast.
Whenever one or more creatures you control deal combat damage to a player, look at the top card of that player's library, then exile it face down. You may play that card for as long as it remains exiled, and mana of any type can be spent to cast that spell.