Lithoform Engine + Corridor Monitor + Mana Echoes

Lithoform Engine

Corridor Monitor

Mana Echoes

How it works

1. Cast Corridor Monitor for 1.
2. While Corridor Monitor is on the stack copy it with Lithoform Engine.
3. Let the token copy resolve.
4. Arrange the triggers for Corridor Monitor and Mana Echoes so Corridor Monitor untaps Lithoform Engine first.
5. Before Mana Echoes resolves copy the original Corridor Monitor with Lithoform engine.
6. Corridor Monitor untaps Lithoform Engine and Mana Echoes adds CCCC.
7. Copy the first Corridor Monitor while its still on the stack.
8. The 3rd Corridor Monitor token untaps Lithoform Engine and adds CCC.
9. Copy Corridor Monitor with Lithoform Engine one more time to net CCCC and untapping Lithoform Engine.
10. Repeat for infinite Corridor Monitors and colorless mana.