Prowling Geistcatcher, Karmic Guide, and Phyrexian Altar

Prerequisites

• Prowling Geistcatcher on the battlefield
• Karmic Guide on the battlefield
• Phyrexian Altar on the battlefield

Steps

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

Results

• Infinite colored mana
• Infinite death triggers
• Infinite ETB
• Infinite LTB
• Infinite sacrifice triggers