Celestial Gatekeeper, Molten Echoes, and Phyrexian Altar

Prerequisites

• Celestial Gatekeeper in hand
• Molten Echoes on the battlefield
• Phyrexian Altar on the battlefield
• "Bird" or "Cleric" chosen with Motlen Echoes
• available

Steps

1. Cast Celestial Gatekeeper by paying
2. Celestial Gatekeeper enters the battlefield, triggering Molten Echoes, creating a token copy of Celestial Gatekeeper with haste
3. Activate Phyrexian Altar by sacrificing the nontoken Celestial Gatekeeper, adding
4. Celestial Gatekeeper dies, triggering itself
5. In response, activate Phyrexian Altar by sacrificing the Celestial Gatekeeper token, adding
6. The Celestial Gateekeeper token dies, triggering itself, exiling itself and returning Celestial Gatekeeper from your graveyard to the battlefield
7. Celestial Gatekeeper enters the battlefield, triggering Molten Echoes, creating a token copy of Celestial Gatekeeper with haste
8. Resolve the nontoken Celestial Gateekeeper's trigger, failing to exile itself and returning up to two more Birds and/or Clerics from your graveyard to the battlefield
9. If you returned a creature of the type chosen with Motlen Echoes, it triggers, creating a token copy of that creature with haste
10. Repeat from step 3

Results

• Infinite blinking of Bird or Cleric creatures
• Infinite colored mana
• Infinite creature tokens with haste
• Infinite death triggers
• Infinite ETB
• Infinite LTB
• Infinite sacrifice triggers