Steward of the Harvest, Umbral Mantle, and Cabal Stronghold

Prerequisites

• Steward of the Harvest on the battlefield
• Umbral Mantle on the battlefield
• Cabal Stronghold in exile
• available

Steps

1. Activate the creature with Umbral Mantle attached using Cabal Stronghold's ability by paying and tapping it, adding at least six
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 black mana
• Infinitely large creature until end of turn