Elemental Mastery, Cathars' Crusade, and Barrenton Medic

Prerequisites

• Elemental Mastery on the battlefield
• Cathars' Crusade on the battlefield
• Barrenton Medic on the battlefield
• Elemental Mastery attached to Barrenton Medic
• Barrenton Medic does not have summoning sickness, and has a power of one or greater

Steps

1. Activate Barrenton Medic by tapping it, creating at least one 1/1 Elemental creature tokens with haste
2. When the Elemental enters the battlefield, Cathars' Crusade triggers, putting a +1/+1 counter on each creature you control
3. Activate Barrenton Medic by putting a -1/-1 counter on it, untapping it
4. Repeat
5. If Barrenton Medic has a power of two or greater, it will also get infinite +1/+1 counters

Results

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