Arcbound Reclaimer + Showdown of the Skalds + Bolas's Citadel + Dark Sphere

Arcbound Reclaimer

Showdown of the Skalds

Bolas's Citadel

Dark Sphere

How it works

1. Cast Dark Sphere either from your hand by paying 0 or from the top of your library by paying 0 life.
2. Showdown of the Skalds triggers, putting a +1/+1 counter on Arcbound Reclaimer.
3. Activate Dark Sphere by tapping and sacrificing it.
4. Activate Arcbound Reclaimer by removing a +1/+1 counter from it, putting Dark Sphere from your graveyard onto the top of your library.
5. Repeat.

This crafty loop turns the life-payment constraint of Bolas's Citadel into a non-issue by letting you cast Dark Sphere for free from the top of your library repeatedly. As each free cast triggers the second and third chapters of Showdown of the Skalds, you can place a +1/+1 counter onto Arcbound Reclaimer. That counter immediately fuels Arcbound Reclaimer's activated ability, allowing you to recycle Dark Sphere right back to the top of your library so the cycle can begin anew.