Cast Cubwarden for its mutate cost by paying {W}{W}, targeting a non-Human creature you control.
The Cubwarden mutated creature triggers, creating two 1/1 Cat creature tokens.
Activate Phyrexian Altar by sacrificing the Cubwarden mutated creature, adding {W}.
When the Cubwarden mutated creature dies, Enduring Renewal triggers, returning Cubwarden and any cards merged with it from your graveyard to your hand.
Activate Phyrexian Altar by sacrificing a Cat token, adding {W}.
Repeat.

Infinite death triggers

Infinite ETB

Infinite LTB

Infinite sacrifice triggers

Infinite storm count

Enduring Renewal

Phyrexian Altar

Cubwarden

Semblance Anvil

Planar Gate

Killian, Ink Duelist

Hamza, Guardian of Arashin

Centaur Omenreader

Cast Cubwarden for its mutate cost by paying {W}{W}.
Animar triggers, putting a +1/+1 counter on itself.
Resolve Cubwarden, targeting a non-Human creature you control.
The Cubwarden mutated creature triggers, creating two 1/1 Cat creature tokens.
Activate Phyrexian Altar by sacrificing the Cubwarden mutated creature, adding {W}.
When the Cubwarden mutated creature dies, Enduring Renewal triggers, returning Cubwarden and any cards merged with it from your graveyard to your hand.
Activate Phyrexian Altar by sacrificing a Cat token, adding {W}.
Repeat.

Infinite +1/+1 counters on a creature

Animar, Soul of Elements

Combos with "Cubwarden"