Crackdown Construct, and Aphetto Alchemist

Prerequisites

• Crackdown Construct on the battlefield
• Aphetto Alchemist on the battlefield
• Aphetto Alchemist does not have summoning sickness

Steps

1. Activate Aphetto Alchemist by tapping it, targeting itself
2. Crackdown Construct triggers, giving itself +1/+1 until end of turn
3. Resolve the Aphetto Alchemist ability, untapping it
4. Repeat

Results

• Infinitely large Crackdown Construct until end of turn