How can you create a combo with Hidetsugu, Devouring Chaos, Intruder Alarm, Mortuary, Walking Ballista?
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[START OF COMBO]This combo can be formed with Hidetsugu, Devouring Chaos, Intruder Alarm, Mortuary, Walking Ballista

Color identity: UBR
Mana cost: 
Steps:
  1. Activate all mana-producing creatures you control by tapping them, adding at least {3}{R}.
  2. Cast Walking Ballista by paying {0}.
  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 {2}{R} 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.[END OF COMBO STEPS]

Result:
  - Infinite +1/+1 counters on Walking Ballista
  - Infinite damage
  - Infinite death triggers
  - Infinite enters the battlefield
  - Infinite leaves the battlefield
  - Infinite mana creatures you control can produce
  - Infinite storm count
  - Infinite untap of all creatures[END OF COMBO RESULT][END OF COMBO]

Other prerequisites:
  - Hidetsugu, Devouring Chaos must be on the battlefield
  - Intruder Alarm must be on the battlefield
  - Mortuary must be on the battlefield
  - Walking Ballista must be in your hand
  - Hidetsugu does not have summoning sickness.
  - Creatures you control can tap to produce at least {3}{R}.
[END OF COMBO PREREQUISITES]
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