Elemental Mastery, Cathars' Crusade, and Devoted Druid

Prerequisites

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

Steps

1. Activate Devoted Druid by tapping it, creating at least two 1/1 Elemental creature tokens with haste
2. When the Elementals enters the battlefield, Cathars' Crusade trigger that many times, putting that many +1/+1 counters on each creature you control
3. Activate Devoted Druid by putting a -1/-1 counter on it, untapping it
4. Repeat
5. If Devoted Druid has a power of two or greater, you then get infinite +1/+1 counters on Devoted Druid, which you may use to activate its mana ability instead to get infinite

Results

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