Cast Spire Golem by paying {0}.
Radagast and Spireroot trigger.
Resolve the Spireroot trigger, adding {G}.
Resolve the Radagast trigger, creating a 3/3 Beast creature token.
Activate Phyrexian Altar by sacrificing the Beast, adding {1}.
Activate Temur Sabertooth by paying {1}{G}, returning Spire Golem from the battlefield to your hand.
Repeat.

Infinite death triggers

Infinite creature ETB

Infinite creature LTB

Infinite creature sacrifice triggers

Infinite storm count

Radagast, Wizard of Wilds

Temur Sabertooth

Phyrexian Altar

Spire Golem

Tangleroot

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

Primal Vigor

Parallel Lives

Adrix and Nev, Twincasters

Doubling Season

Combos with "Spire Golem"