Derevi, Empyrial Tactician + Mycosynth Lattice + City of Shadows + Panharmonicon

Derevi, Empyrial Tactician

Mycosynth Lattice

City of Shadows

Panharmonicon

How it works

1. Activate Derevi's ability to put him onto the battlefield from the command zone.
2. Target City of Shadows with both Derevi's enter the battlefield ability and the copy of that ability from Panharmonicon.
3. When the copy of Derevi's trigger untaps City of Shadows, activate City of Shadows' first ability, exiling Derevi.
4. Elect to put Derevi in the command zone.
5. When Derevi's trigger untapping City of Shadows, activate City of Shadows' second ability to add mana.
6. Repeat.