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One easy example is Death's Shadow decks in Modern
SET/SERIES: POKEMON SUN AND MOON (BLACK STAR PROMO)
When you cast a creature for its mutate cost, it's still considered being cast, and many are multicolored
For example, check out this W/R Tokens deck: Creatures (21) 4 Precinct Captain 2 Sunhome Guildmage 2 Ogre Battledriver 2 Purphoros, God of the Forge 4 Soldier of the Pantheon 4 Brimaz, King of Oreskos 3 Eidolon of Countless Battles Planeswalkers (3) Lands (27) Spells (9) We could totally maindeck Revoke Existence, but every reactive card is one less creature to get pumped by Spear of Heliod, Eidolon of Countless Battles, Ogre Battledriver, Purphoros, and Sunhome Guildmage