Thopter Squadron + Dross Scorpion + Coveted Jewel

Thopter Squadron

Dross Scorpion

Coveted Jewel

How it works

1. Activate Coveted Jewel by tapping it, adding three mana of any one color.
2. Activate Thopter Squadron first ability by paying 1 and removing +1/+1 counter, creating a 1/1 Thopter token.
3. Activate Thopter Squadron second ability by paying 1 and sacrificing a Thopter, putting a +1/+1 counter on itself.
4. Dross Scorpion triggers, untapping Coveted Jewel.
5. Repeat.