Blessed Breath

Protection from the color of your choice on one of your creatures is a one-mana combat trick with a deliberately narrow window: it stops the damage a blocker would deal, lets an attacker connect unblocked, or shrugs off a single-color removal spell at the moment it would resolve. Cast bare, that is serviceable defense and nothing more. The lift comes from the splice rider, which lets you reveal this from hand while another Arcane spell is already heading to the stack and pay the white cost, bolting the protection effect onto a cast that was happening anyway. That is the premise of the whole Arcane engine: cheap, modular clauses that ride a single cast and turn one spell into a chain without paying card disadvantage for every link. Protection is a near-ideal clause to attach, because it resolves combat and targeting math in one stroke (dodging damage, blocks, and single-color removal at once), and because it arrives at the exact instant an opponent commits a removal spell. Played alone, it is a defensive instant with a tight use case. Folded into a chain, it becomes the safety valve that keeps the creature carrying the rest of the Arcane sequence alive, which is the role the design was built around.