Prowling Geistcatcher + Karmic Guide + Phyrexian Altar

Prowling Geistcatcher

Karmic Guide

Phyrexian Altar

How it works

1. Activate Phyrexian Altar by sacrificing Karmic Guide, adding one mana of any color.
2. When Karmic Guide dies, Prowling Geistcatcher's first ability triggers, exiling Karmic Guide from your graveyard.
3. Activate Phyrexian Altar by sacrificing Prowling Geistcatcher, adding one mana of any color.
4. When Prowling Geistcatcher dies, its second ability triggers, returning Karmic Guide from exile to the battlefield.
5. When Karmic Guide enters the battlefield, it triggers, returning Prowling Geistcatcher from your graveyard to the battlefield.
6. Repeat.

This elegant loop turns a graveyard into an engine by cycling your creatures back and forth through exile and the battlefield. You begin by using Phyrexian Altar to sacrifice Karmic Guide, which triggers Prowling Geistcatcher to cleanly tuck the angel away into exile rather than letting it linger in the graveyard. Once you then sacrifice Prowling Geistcatcher to the Altar as well, its leave-the-battlefield trigger releases Karmic Guide right back to the battlefield, whose own entry trigger immediately fishes Prowling Geistcatcher out of the graveyard to reset the whole cycle.