Trusty Boomerang + Mana Echoes + Nahiri's Resolve + Barret, Avalanche Leader

Trusty Boomerang

Mana Echoes

Nahiri's Resolve

Barret, Avalanche Leader

How it works

1. Cast Trusty Boomerang by paying 1.
2. When Trusty Boomerang enters, Barret's triggers, creating a 2/2 Rebel creature token.
3. When the Rebel enters, Mana Echoes triggers, adding C for each Rebel you control.
4. Activate Trusty Boomerang's equip ability by paying 1, attaching it to the Rebel token.
5. Activate the Rebel by paying 1 and tapping it, tapping a creature and returning Trusty Boomerang from the battlefield to your hand.
6. Repeat.