Isochron Scepter + Energy Arc + Karn, Silver Golem

Isochron Scepter

Energy Arc

Karn, Silver Golem

How it works

1. Activate Karn by paying 1, causing Isochron Scepter to become an artifact creature until end of turn.
2. Activate creatures you control by tapping those, adding 3.
3. Activate Isochron Scepter by paying 2 and tapping it, casting a copy of Energy Arc without paying its mana cost, untapping all creatures.
4. Repeat from step 2.