How can you create a combo with Xavier Sal, Infested Captain, Intruder Alarm, First Day of Class?
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[START OF COMBO]This combo can be formed with Xavier Sal, Infested Captain, Intruder Alarm, First Day of Class

Color identity: UBRG
Mana cost: {1}{R}
Steps:
  1. Cast First Day of Class by paying {1}{R}.
  2. Activate Xavier Sal's first ability by tapping it and removing a counter from a permanent you control, creating a copy of any creature token you control.
  3. When the creature token enters the battlefield, Intruder Alarm and First Day of Class trigger.
  4. Resolve the Intruder Alarm trigger, untapping all creatures.
  5. Resolve the First Day of Class trigger, putting a +1/+1 counter on the creature token.
  6. Repeat.[END OF COMBO STEPS]

Result:
  - Infinite creature tokens
  - Infinite enters the battlefield
  - Infinite mana creatures you control can produce
  - Infinite untap of all creatures
  - Infinite creatures tokens with haste[END OF COMBO RESULT][END OF COMBO]

Other prerequisites:
  - Xavier Sal, Infested Captain must be on the battlefield
  - Intruder Alarm must be on the battlefield
  - First Day of Class must be in your hand
  - There is at least one counter on a permanent you control.
  - You control at least one creature token.
[END OF COMBO PREREQUISITES]
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