Steward of the Harvest, Umbral Mantle, and Serra's Sanctum

Prerequisites

• Steward of the Harvest on the battlefield
• Umbral Mantle on the battlefield
• Serra's Sanctum in exile

Steps

1. Activate the creature with Umbral Mantle attached using Serra's Sanctum's ability by tapping it, adding at least
2. Activate the creature by paying and untapping it, giving it +2/+2 until end of turn
3. Repeat

Results

• Infinite untap of creatures you control
• Infinite mana creatures you control can produce
• Infinite white mana
• Infinitely large creature until end of turn