At the beginning of your upkeep, Mayael's Aria triggers.
Holding priority, cast Grand Crescendo by paying ({5} magic symbol) ({W} magic symbol) ({W} magic symbol) , creating five 1/1 Citizen creature tokens.
When the Citizens enter the battlefield, Devilish Valet triggers that many times, doubling its power that many times, causing its power to be at least 32 until end of turn.
Resolve the Mayael's Aria trigger, causing you to put a +1/+1 counter on each creature you control, gain 10 life and win the game.