Stalwart Successor, Phyrexian Altar, and Trapjaw Kelpie

Prerequisites

• Stalwart Successor on the battlefield
• Phyrexian Altar on the battlefield
• Trapjaw Kelpie on the battlefield

Steps

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

Results

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