Myr Welder, Umbral Mantle, and Chromatic Orrery

Prerequisites

• Myr Welder on the battlefield
• Umbral Mantle on the battlefield
• Chromatic Orrery in exile

Steps

1. Activate Myr Welder using Chromatic Orrery's ability by tapping it, adding
2. Activate Myr Welder by paying and untapping it, giving it +2/+2 until end of turn
3. Repeat

Results

• Infinite untap of creatures you control
• Infinite colorless mana
• Infinite card draw
• Infinite draw triggers
• Infinitely large creature until end of turn