The Watcher in the Water, Symmetry Matrix, and Ashnod's Altar

Prerequisites

• The Watcher in the Water on the battlefield
• Symmetry Matrix on the battlefield
• Ashnod's Altar 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 triggers
4. Holding priority, activate Ashnod's Altar by sacrificing the Tentacle, adding
5. When the Tentacle dies, The Watcher's second ability triggers, untapping up to one Kraken you control
6. Resolve the Symmetry Matrix trigger, causing you to pay to draw a card
7. 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
• Near-infinite untap of Krakens you control