Stalwart Successor + Phyrexian Altar + Trapjaw Kelpie

Stalwart Successor

Phyrexian Altar

Trapjaw Kelpie

How it works

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. When Trapjaw Kelpie enters, Stalwart Successor triggers, putting a +1/+1 counter on Trapjaw Kelpie
4. Repeat.

This clever loop revolves around Trapjaw Kelpie and its persist ability, which normally would exhaust itself after a single recursion due to the -1/-1 counter it returns with. However, Stalwart Successor solves this limitation completely: the moment the Kelpie reenters the battlefield, the Successor's triggered ability rewards that first instance of counters by placing a +1/+1 counter on it. Thanks to rules of state-based actions, the opposing +1/+1 and -1/+1 (or -1/-1) counters annihilate each other, leaving the Kelpie completely clean and ready to persist all over again. By feeding this resilient beast to Phyrexian Altar along the way, you turn the eternal cycle into an infinite stream of colored mana and boundless death triggers.