Zirda, the Dawnwaker + Grim Monolith

Zirda, the Dawnwaker
Grim Monolith

Requires
All permanents on the battlefield.
Steps
  1. Activate Grim Monolith's first ability by tapping it, adding ccc
  2. Activate Grim Monolith's second ability by paying 2, untapping it
  3. Repeat
Results
Infinite colorless mana.