Necrotic Ooze, Stern Marshal, and Devoted Druid

Prerequisites

• Necrotic Ooze on the battlefield
• Stern Marshal in the graveyard
• Devoted Druid in the graveyard
• Necrotic Ooze does not have summoning sickness
• It is your precombat main phase

Steps

1. During your precombat main phase, activate Necrotic Ooze using Stern Marshal's ability by tapping it, giving it +2/+2 until end of turn
2. Activate Necrotic Ooze using Devoted Druid's second ability by putting a -1/-1 counter on it, untapping it
3. Repeat
4. Once Necrotic Ooze has infinite toughness, you may instead use Devoted Druid's first ability to get infinite green mana

Results

• Infinite green mana
• Infinitely large Necrotic Ooze until end of turn