Dimir Aqueduct + PuPu UFO + Elven Raft-Steerer

Dimir Aqueduct

PuPu UFO

Elven Raft-Steerer

How it works

1. Activate PuPu UFO by tapping it, putting Dimir Aqueduct from your hand onto the battlefield.
2. When Dimir Aqueduct enters the battlefield, it and Elven Raft-Steerer trigger.
3. Resolve the Dimir Aqueduct trigger, returning itself from the battlefield to your hand.
4. Resolve the Elven Raft-Steerer trigger, untapping PuPu UFO.
5. Repeat.