At the beginning of your upkeep, Mayael's Aria triggers.
Holding priority, activate Emergence Zone's second ability by paying ({1} magic symbol) and tapping it, allowing you to cast all spells this turn as though they have flash.
Cast Avenger of Zendikar by paying ({5} magic symbol) ({G} magic symbol) ({G} magic symbol) .
Avenger of Zendikar enters the battlefield, triggering itself and Devilish Valet.
Resolve the Avenger of Zendikar trigger, creating a 0/1 Plant creature token for each land you control.
Each Plant token enters the battlefield, triggering Devilish Valet that many times.
Resolve a Devilish Valet trigger, doubling its power until end of turn.
Repeat step 7 for each remaining Devilish Valet trigger.
Resolve the Mayael's Aria trigger, causing you to put a +1/+1 counter on each creature you control, gain ten life and win the game.
Results
Near-infinitely powerful Devilish Valet until end of turn.
Win the game at the beginning of your next upkeep.