Trusty Boomerang + Mana Echoes + Wartime Protestors + Sokka and Suki

Trusty Boomerang

Mana Echoes

Wartime Protestors

Sokka and Suki

How it works

1. Cast Trusty Boomerang by paying 1.
2. When Trusty Boomerang enters, Sokka and Suki's second ability triggers, creating a 1/1 Ally creature token.
3. When the Ally enters, Sokka's first ability, Wartime Protestors and Mana Echoes trigger.
4. Resolve the Mana Echoes trigger, adding C for each Ally you control.
5. Resolve the Sokka trigger, attaching Trusty Boomerang to the Ally token.
6. Resolve the Wartime Protestors trigger, putting a +1/+1 counter on the Ally token and giving it haste until end of turn.
7. Activate the Ally by paying 1 and tapping it, tapping a creature and returning Trusty Boomerang from the battlefield to your hand.
8. Repeat.