Halo Fountain, Phyrexian Altar, and Karn, the Great Creator

Prerequisites

• Halo Fountain on the battlefield
• Phyrexian Altar on the battlefield
• Karn, the Great Creator on the battlefield
• Halo Fountain does not have summoning sickness
• available

Steps

1. Activate Karn's first loyalty ability by putting a loyalty counter on it, causing Halo Fountain to become an artifact creature until end of turn
2. Activate Halo Fountain's first ability by paying , tapping it and untapping it, creating a 1/1 Citizen creature token
3. Activate Phyrexian Altar by sacrificing the Citizen, adding
4. Repeat from step 2

Results

• Infinite death triggers
• Infinite ETB
• Infinite LTB
• Infinite sacrifice triggers