Radagast, Wizard of Wilds + Temur Sabertooth + Phyrexian Altar + Mycosynth Golem + Primal Vigor

Radagast, Wizard of Wilds

Temur Sabertooth

Phyrexian Altar

Mycosynth Golem

Primal Vigor

How it works

1. Cast Mycosynth Golem by paying 0.
2. Radagast triggers, creating two 3/3 Beast creature tokens.
3. Activate Phyrexian Altar twice by sacrificing the Beasts, adding 1.
4. Activate Temur Sabertooth by paying 1, returning Mycosynth Golem from the battlefield to your hand.
5. Repeat.

This brilliant loop centers on casting Mycosynth Golem for free thanks to its affinity for artifacts, which conveniently triggers Radagast, Wizard of Wilds to reward your high-mana-value spell cast. While Radagast's trigger would normally make just a pair of tokens, Primal Vigor doubles that output into four tokens, providing plenty of fodder to sacrifice to Phyrexian Altar for the exact mana needed to fuel the engine. Finally, you use that generated mana to activate Temur Sabertooth's ability to bounce the Golem right back to your hand, allowing you to replay it and repeat the cycle indefinitely.