The Watcher in the Water, Symmetry Matrix, and Mana Echoes

Prerequisites

• The Watcher in the Water on the battlefield
• Symmetry Matrix on the battlefield
• Mana Echoes on the battlefield
• You have a way to draw a card during an opponent's turn

Steps

1. Draw a card during an opponent's turn
2. The Watcher's first ability riggers, creating a 1/1 Tentacle creature token
3. When the Tentacle enters the battlefield, Symmetry Matrix and Mana Echoes trigger
4. Resolve the Mana Echoes trigger, adding for each Tentacle on the battlefield
5. Resolve the Symmetry Matrix trigger, causing you to pay to draw a card
6. Repeat from step 2

Results

• Infinite card draw
• Infinite draw triggers
• Near-infinite colorless mana
• Near-infinite creature tokens
• Near-infinite death triggers
• Near-infinite ETB
• Near-infinite LTB
• Near-infinite sacrifice triggers