Bellowing Aegisaur, and Walking Ballista

Prerequisites

• Bellowing Aegisaur on the battlefield
• Walking Ballista on the battlefield
• Walking Ballista has at least two +1/+1 counters
• You have a way to give Bellowing Aegisaur indestructible

Steps

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

Results

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