Kenrith, the Returned King + Phyrexian Altar + Deranged Hermit

Kenrith, the Returned King

Phyrexian Altar

Deranged Hermit

How it works

1. Activate Kenrith's fifth ability by paying 4, returning Deranged Hermit to the battlefield from your graveyard.
2. When Deranged Hermit enters the battlefield, it triggers, creating four 1/1 Squirrel creature tokens.
3. Activate Phyrexian Altar five times by sacrificing Deranged Hermit and the four Squirrel tokens, adding 4.
4. Repeat.

This loop is elegantly fueled by Phyrexian Altar, which converts any creature into the exact black mana needed to keep the cycle turning. You use that sacrifice outlet to feed Kenrith, the Returned King's black-mana resurrection ability, paying {4}{B} to pull Deranged Hermit right back out of your graveyard. Each time Deranged Hermit returns, its entrance triggers a burst of token generation that immediately provides fresh fodder for the Altar, generating a net surplus of sacrifices to feed the engine indefinitely.