Exchange of Words, Devoted Druid, and Lair of the Hydra

Prerequisites

• Exchange of Words in hand
• Devoted Druid on the battlefield
• Lair of the Hydra on the battlefield
• Lair of the Hydra does not have summoning sickness
• available

Steps

1. Activate Lair of the Hydra's last ability by paying , making it a 1/1 land creature until end of turn
2. Cast Exchange of Words by paying
3. Exchange of Words enters the battlefield, exchanging the text boxes of Devoted Druid and Lair of the Hydra
4. As the turn ends, Lair of the Hydra stops being a creature
5. On your opponent's upkeep, activate Lair of the Hydra using Devoted Druid's first ability by tapping it, adding
6. Activate Lair of the Hydra using Devoted Druid's last ability, putting a -1/-1 counter on it and untapping it
7. Repeat from step 5

Results

• Infinite green mana
• Infinitely large creature