Shimmer Myr

Flash
You may cast artifact spells as though they had flash.

Foundry Inspector

Artifact spells you cast cost {1} less to cast.

Umori, the Collector

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} as a sorcery.)
As Umori, the Collector enters, choose a card type.
Spells you cast of the chosen type cost {1} less to cast.

Etherium Sculptor

Palladium Myr

Jhoira's Familiar

Flying
Historic spells you cast cost {1} less to cast. (Artifacts, legendaries, and Sagas are historic.)