Hidetsugu, Devouring Chaos, Intruder Alarm, Mortuary, and Walking Ballista

Prerequisites

• Hidetsugu, Devouring Chaos on the battlefield
• Intruder Alarm on the battlefield
• Mortuary on the battlefield
• Walking Ballista in hand
• Hidetsugu does not have summoning sickness
• Creatures you control can tap to produce at least

Steps

1. Activate all mana-producing creatures you control by tapping them, adding at least
2. Cast Walking Ballista by paying
3. Walking Ballista enters the battlefield and dies as a state-based action due to having zero toughness
4. Intruder Alarm and Mortuary trigger
5. Resolve the Intruder Alarm trigger, untapping all creatures
6. Resolve the Mortuary trigger, putting Walking Ballista on top of your library from your graveyard
7. Activate Hidetsugu's second ability by paying and tapping it, exiling Walking Ballista from the top of your library and allowing you cast it this turn
8. Repeat an arbitrarily large number of times
9. Cast Walking Ballista from exile by paying an arbitrarily large amount of mana, causing Walking Ballista to enter with half that many +1/+1 counters on it
10. Activate Walking Ballista's second ability by removing a +1/+1 counter from it, dealing 1 damage to any target
11. Repeat step 10

Results

• Infinite +1/+1 counters on Walking Ballista
• Infinite damage
• Infinite death triggers
• Infinite ETB
• Infinite LTB
• Infinite mana creatures you control can produce
• Infinite storm count
• Infinite untap of all creatures