Brine Elemental, and Vesuvan Shapeshifter

Prerequisites

• Brine Elemental on the battlefield
• Vesuvan Shapeshifter on the battlefield
• Brine Elemental is face up
• Vesuvan Shapeshifter is face down
• available

Steps

1. Turn Vesuvan Shapeshifter face-up for
2. As it turns face up, have it copy Brine Elemental, triggering Brine Elemental's face-up ability
3. Resolve the ability; each opponent skips their next untap step
4. Pass the turn; on your upkeep, turn Vesuvan Shapeshifter face down
5. Repeat infinitely

Results

• Each opponent skips their untap steps indefinitely