Ertha Jo, Frontier Mentor, and Tidewater Minion

Prerequisites

• Ertha Jo, Frontier Mentor on the battlefield
• Tidewater Minion on the battlefield

Steps

1. Activate Tidewater Minion's second ability by tapping it, targeting itself
2. Ertha Jo's second ability triggers, copying Tidewater Minion's ability, targeting any other permanent
3. Resolve both Tidewater Minion abilities, untapping it and the other targeted permanent Repeat

Results

• Infinite mana permanents you control can produce
• Infinite untap of permanents you control