Urban Daggertooth, and Walking Ballista

Prerequisites

• Urban Daggertooth on the battlefield
• Walking Ballista on the battlefield
• Urban Daggertooth has at least one +1/+1 counter
• Walking Ballista has at least two +1/+1 counters

Steps

1. Activate Walking Ballista's second ability by removing a +1/+1 counter from it, dealing 1 damage to Urban Daggertooth
2. Urban Daggertooth triggers, putting a +1/+1 counter on itself and Walking Ballista
3. Repeat

Results

• Infinite +1/+1 counters on Urban Daggertooth
• Infinite proliferate