Phyrexian Altar, Trapjaw Kelpie, and Hardened Academic

Prerequisites

• Phyrexian Altar on the battlefield
• Trapjaw Kelpie on the battlefield
• Hardened Academic on the battlefield

Steps

1. Activate Phyrexian Altar by sacrificing Trapjaw Kelpie
2. When Trapjaw Kelpie dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it
3. Hardened Academic triggers, putting a +1/+1 counter on Trapjaw Kelpie
4. Repeat

Results

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