Marina Vendrell, Ghostly Dancers, and Intruder Alarm

Prerequisites

• Marina Vendrell on the battlefield
• Ghostly Dancers on the battlefield
• Intruder Alarm on the battlefield
• The Room has one half locked, and the other half unlocked
• Creatures you control can tap to produce enough mana to unlock the locked Room
• Marina does not have summoning sickness

Steps

1. Activate any number of creatures you control by tapping them, adding at least enough mana to unlock a locked Room you control
2. Unlock any Room you control by paying its mana cost
3. Ghostly Dancers' second ability triggers, creating a 3/1 Spirit creature token
4. When the Spirit enters the battlefield, Intruder Alarm triggers, untap all creatures
5. Activate Marina by tapping it, locking the Room that was unlocked in step 1
6. Repeat

Results

• Infinite ETB
• Infinite creature tokens
• Infinite untap of all creatures
• Infinite mana creatures you control can produce
• Infinite unlocking of Rooms you control