Combo Devoted Druid +Umbral Mantle +Immaculate Magistrate
You need at least 4 elves in play for this combo to work. Equip Immaculate Magistrate with Umbral Mantle and tap it to add 4 +1/+1 counters to Devoted Druid. Tap Devoted Druid to add one mana and put a -1/-1 counter to untap it. +1/+1 and -1/-1 counters cancel each other out, so repeat the process for a total of 4 mana. Use 3 mana to untap Immaculate Magistrate. Repeat the process for infinite mana. With Infinite Mana, you can build an army of creatures with infinite power with Immaculate Magistrate.