Even without going infinite, being able to untap every turn with Murkfiend Liege, Drumbellower, White Plume Adventurer or Quest for Renewal generates a ton of advantage in multiplayer Commander
Amethyst decks now have an extra, better top-deck game-winner outside of Merlin Goat
UPDATE: Ramp is Really Important One resounding truth when trying to win with the self-mill version of this deck is that you need a ton of mana to execute your winning sequences
Use Condemn and Pacifism to stop your opponents' threatening creatures or Mind Control to gain control of one
This card helps fill the hole in reds removal suite but it does basically the exact same thing as Command the Storm, only better (+1 card is better than +1 damage most of the time), meaning Izzet mages will be overloaded with options at five mana
If the permanent that was turned face up is no longer on the battlefield when Sumala Sentry's triggered ability resolves, you'll still put a +1/+1 counter on Sumala Sentry