2When Volcano Hellion enters the battlefield, it triggers.
3Holding priority, activate Vault of the Archangel's second ability by paying and tapping it, giving creatures you control deathtouch and lifelink until end of turn.
4Resolve the Volcano Hellion trigger, dealing an arbitrarily large amount of damage to you and Volcano Hellion, and causing you to gain twice that much life due to Volcano Hellion's lifelink.