Other creatures you control can tap to produce enough mana to cast both creatures mentioned above after being tapped twice.
Steps
Activate any number of creatures you control by tapping them, adding an amount of mana.
Cast the creature from your hand by paying its mana cost.
Hullbreaker Horror triggers, returning another creature from the battlefield to your hand.
Resolve the creature spell. When it enters,
Intruder Alarm triggers, untapping all creatures.
Repeat.
Notes
Ideally, if the two creatures require different amounts of mana, you will want to start the combo with the lower cost creature in your hand. This should negate the need to start with mana. However, the opposite can be done if you provide mana (as needed) to cover the difference. An example of the prerequisite: If the creatures have total cost , other creatures you control, after tapping two times each, must produce at least . Therefore, if creatures you control can tap to produce at least , they will create after being tapped twice, and meet the prerequisite.
Results
Infinite mana creatures you control can produce.
Infinite storm count.
Infinite untap of creatures.
Infinite creature ETB.
Infinite creature LTB.
Metadata
Bracket tag
SpicyBracket 3-4+
Probably 3 or 4, but hard to classify
1
2
3
4
5
1 · Exhibition5 · cEDH
Bracket tags are estimated from the cards and results of each combo, as a guideline rather than a strict classification.