Construction Arsonist

Alchemy: Murders at Karlov Manor (YMKM) #15 · Rare · Creature — Goblin Rogue Wizard

Mana cost: {1}{R}

When Construction Arsonist enters, you may choose an instant or sorcery card in your hand. If you do, that card perpetually incorporates {R} and gains "When you cast this spell, it deals 2 damage to each opponent."
Whenever you cast a multicolored spell, Construction Arsonist gets +1/+1 until end of turn for each of that spell's colors.