How can you create a combo with Royal Assassin, Urabrask the Hidden, Intruder Alarm?
user
[START OF COMBO]This combo can be formed with Royal Assassin, Urabrask the Hidden, Intruder Alarm

Color identity: UBR
Mana cost: 
Steps:
  1. Whenever a creature enters the battlefield under an opponent's control, it enters tapped due to Urabrask and triggers Intruder Alarm.
  2. Holding priority, activate Royal Assassin by tapping it, destroying the creature.
  3. Resolve the Intruder Alarm trigger, untapping all creatures.
  4. Repeat.[END OF COMBO STEPS]

Result:
  - Destroy all creatures that enter the battlefield under an opponent's control[END OF COMBO RESULT][END OF COMBO]

Other prerequisites:
  - All permanants must be on the battlefield
[END OF COMBO PREREQUISITES]
assistant