Umori, the Collector [Ikoria: Lair of Behemoths Prerelease Promos]

Companion — Each nonland card in your starting deck shares a card type. (If this card is your chosen companion, you may put it into your hand from outside the game for {3} any time you could cast a sorcery.)
As Umori, the Collector enters the battlefield, choose a card type.
Spells you cast of the chosen type cost {1} less to cast.