Crackdown Construct, and Dragonfire Blade

Prerequisites

• Crackdown Construct on the battlefield
• Dragonfire Blade on the battlefield

Steps

1. Activate Dragonfire Blade's equip ability by paying , targeting any creature you control that's four or more colors
2. Crackdown Construct triggers, giving it +1/+1 until end of turn
3. Resolve Dragonfire Blade's equip ability
4. Repeat

Results

• Infinitely large Crackdown Construct until end of turn