Agatha's Soul Cauldron, Walking Ballista, and Nearheath Stalker

Prerequisites

• Agatha's Soul Cauldron on the battlefield
• Walking Ballista in exile
• Nearheath Stalker on the battlefield
• Nearheath Stalker has at least one +1/+1 counter on it

Steps

1. Activate Nearheath Stalker using Walking Ballista's second ability by removing a +1/+1 counter from it
2. Repeat step 1 until Nearheath Stalker has no +1/+1 counters on it
3. Resolve all Nearheath Stalker abilities dealing 1 damage to Nearheath Stalker, and any remaining damage to any target(s)
4. Nearheath Stalker dies as a state-based action due to having 0 toughness
5. Nearheath Stalker's undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it
6. Repeat

Results

• Infinite death triggers
• Infinite ETB
• Infinite LTB