Rings of Brighthearth + Forsaken Monument + Grim Monolith

Rings of Brighthearth

Forsaken Monument

Grim Monolith

How it works

1. Activate Grim Monolith's first ability by tapping it, adding CCC.
2. Forsaken Monument triggers, adding C.
3. Activate Grim Monolith's second ability by paying 4.
4. Rings of Brighthearth triggers, causing you to pay 2 to copy Grim Monolith's ability.
5. Resolve the first Grim Monolith ability, untapping it.
6. Activate Grim Monolith's first ability by tapping it, adding CCC.
7. Forsaken Monument triggers, adding C.
8. Resolve the second Grim Monolith ability from step 3, untapping it.
9. Repeat.