Sun Titan + Karmic Guide + Animate Dead + Phyrexian Altar

Sun Titan

Karmic Guide

Animate Dead

Phyrexian Altar

How it works

1. Cast Sun Titan.
2. Sun Titan enters the battlefield, returning Animate Dead from your graveyard to the battlefield.
3. With the Animate Dead trigger on the stack, Activate Phyrexian Altar, sacrificing Sun Titan to add a mana of any color.
4. Resolve the Animate Dead trigger, causing it to become an Aura with "enchant creature put onto the battlefield with Animate Dead" and returning Karmic Guide from your graveyard to the battlefield.
5. Animate Dead is put into your graveyard due to state based actions, as it cannot attach to a creature with protection from black.
6. Animate Dead triggers, causing you to sacrifice Karmic Guide.
7. Karmic Guide's enter the battlefield triggers.
8. Resolve Karmic Guide's enter the battlefield trigger returning Sun Titan from your graveyard to the battlefield.
9. Repeat from step 2.