Give Bellowing Aegisaur indestructible by any method.
Activate Walking Ballisata by removing a +1/+1 counter from it, dealing 1 damage to Bellowing Aegisaur.
Bellowing Aegisaur triggers, putting a +1/+1 counter on each other creature you control.
Repeat from step 2.

Infinite +1/+1 counters on all creatures you control except Walking Ballista and Bellowing Aegisaur

Bellowing Aegisaur

Walking Ballista

Give Bellowing Aegisaur indestructible by any method.
Activate Triskelion by removing a +1/+1 counter from it, dealing 1 damage to Bellowing Aegisaur.
Bellowing Aegisaur triggers, putting a +1/+1 counter on each other creature you control.
Repeat from step 2.

Infinite +1/+1 counters on all creatures you control except Triskelion and Bellowing Aegisaur

Triskelion

Give Bellowing Aegisaur indestructible by any method.
Deal damage to Bellowing Aegisaur.
Bellowing Aegisaur triggers, putting a +1/+1 counter on each other creature you control.
Scurry Oak triggers, creating a 1/1 Squirrel creature token.
The Squirrel enters the battlefield, triggering Warstorm Surge, dealing 1 damage to Bellowing Aegisaur.
Repeat from step 3.

Infinite +1/+1 counters on all creatures you control except Bellowing Aegisaur

Infinite creature tokens

Infinite ETB

Scurry Oak

Warstorm Surge

Give Bellowing Aegisaur indestructible by any method.
Deal damage to Bellowing Aegisaur.
Bellowing Aegisaur triggers, putting a +1/+1 counter on each other creature you control.
Scurry Oak triggers, creating a 1/1 Squirrel creature token.
The Squirrel enters the battlefield, triggering Terror of the Peaks, dealing 1 damage to Bellowing Aegisaur.
Repeat from step 3.

Terror of the Peaks

Cast Electroduplicate by paying its mana cost, creating a token copy of Bellowing Aegisaur.
Activate a mana-producing permanent you control by tapping it, adding at least {G}.
Activate Wayta by paying {G} and tapping it, causing Cacophodon and the nontoken Bellowing Aegisaur to fight each other, with each only taking 1 damage due to Temple Altisaur.
Cacophodon and Bellowing Aegisaur each trigger twice.
Resolve all Bellowing Aegisaur triggers, putting two +1/+1 counters on each other creature you control.
Resolve both Cacophodon triggers, untapping the mana-producing permanent and Wayta.
Repeat from step 2, alternating between having the token and nontoken Bellowing Aegisaur fight Cacophodon.

Infinite +1/+1 counters

Wayta, Trainer Prodigy

Cacophodon

Temple Altisaur

Electroduplicate

Give Bellowing Aegisaur indestructible by any method.
Deal damage to Bellowing Aegisaur.
Bellowing Aegisaur triggers, putting a +1/+1 counter on each other creature you control.
Scurry Oak triggers, creating a 1/1 Squirrel creature token.
The Squirrel enters the battlefield, triggering Pandemonium, dealing 1 damage to Bellowing Aegisaur.
Repeat from step 3.

Pandemonium

Activate a mana-producing permanent you control by tapping it, adding at least {G}.
Activate Wayta by paying {G} and tapping it, causing Cacophodon and Bellowing Aegisaur to fight each other, with each only taking 1 damage due to Temple Altisaur.
Cacophodon and Bellowing Aegisaur trigger twice.
Resolve both Bellowing Aegisaur triggers, putting two +1/+1 counters on each creature you control.
Resolve both Cacophodon triggers, untapping the mana-producing permanent and Wayta.
Repeat from step 2, alternating between having Cacophodon fight Bellowing Aegisaur and Progenitor Mimic to ensure neither dies due to lethal damage.

Progenitor Mimic

Give Bellowing Aegisaur indestructible by any method.
Deal damage to Bellowing Aegisaur, with all but 1 of that damage being prevented by Temple Altisaur.
Bellowing Aegisaur, Ghyrson Starn, and Spark Double trigger.
Resolve the Spark Double trigger, dealing 2 damage to any target.
Resolve the Ghyrson Starn trigger, dealing 2 damage to Bellowing Aegisaur, with all but 1 of that damage being prevented by Temple Altisaur.
Spark Double and Bellowing Aegisaur trigger.
Resolve the Bellowing Aegisaur trigger, putting a +1/+1 counter on each other creature you control.
Resolve the Spark Double trigger, dealing 2 damage to Bellowing Aegisaur, with all but 1 of that damage being prevented by Temple Altisaur.
Ghyrson Starn and Bellowing Aegisaur trigger.
Repeat from step 5.

Combos with "Bellowing Aegisaur"