When Volcano Hellion enters the battlefield, it triggers.
Holding priority, activate Vault of the Archangel's second ability by paying ({2} magic symbol) ({W} magic symbol) ({B} magic symbol) and tapping it, giving creatures you control deathtouch and lifelink until end of turn.
Resolve 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.