Lae'zel, Vlaakith's Champion, Druid's Call, Cathars' Crusade, and Walking Ballista

Prerequisites

• Lae'zel, Vlaakith's Champion on the battlefield
• Druid's Call on the battlefield
• Cathars' Crusade on the battlefield
• Walking Ballista on the battlefield
• Druid's Call attached to Walking Ballista
• Walking Ballista has at least three +1/+1 counters

Steps

1. Activate Walking Ballista's first ability by removing a +1/+1 counter from it, dealing 1 damage to itself
2. Druid's Call triggers, creating a 1/1 Squirrel creature token
3. The Squirrel enters the battlefield, triggering Cathars' Crusade, putting two +1/+1 counters on each creature you control
4. Repeat

Results

• Infinite +1/+1 counters
• Infinite creature tokens
• Infinite ETB