Gemstone Array + Crackdown Construct + Forensic Gadgeteer

Gemstone Array

Crackdown Construct

Forensic Gadgeteer

How it works

1. Activate Gemstone Array's first ability by paying 1.
2. Crackdown Construct triggers, getting +1/+1 until end of turn.
3. Resolve Gemstone Array's ability, putting a charge counter on it.
4. Activate Gemstone Array's second ability by removing a charge counter from it, adding 1.
5. Repeat.