Adarkar Valkyrie + Intruder Alarm + Moritte of the Frost

Adarkar Valkyrie

Intruder Alarm

Moritte of the Frost

How it works

1. Activate Adarkar Valkyrie by tapping it, targeting any legendary creature you control.
2. Cast Moritte of the Frost by paying 2, choosing to have it enter the battlefield as a copy of the legendary creature targeted in step 1.
3. Put the legendary creature into your graveyard due to the legend rule.
4. Adarkar Valkyrie and Intruder Alarm trigger.
5. Resolve the Intruder Alarm trigger, untapping all creatures.
6. Holding priority, activate Adarkar Valkyrie by tapping it, targeting Moritte of the Frost.
7. Resolve the Adarkar Valkyrie trigger from step 4, returning the legendary creature to the battlefield from your graveyard.
8. Put Moritte of the Frost into your graveyard due to the legend rule.
9. Adarkar Valkyrie and Intruder Alarm trigger.
10. Resolve the Intruder Alarm trigger, untapping all creatures.
11. Holding priority, activate Adarkar Valkyrie by tapping it, targeting the legendary creature.
12. Resolve the Adarkar Valkyrie trigger from step 9, returning Moritte of the Frost to the battlefield from your graveyard as a copy of the legendary creature.
13. Repeat from step 3.

This elegant loop relies on the constant state-based sacrifice of the legend rule to repeatedly trigger Adarkar Valkyrie's delayed return ability. By having Moritte of the Frost enter as a copy of your chosen legendary creature, you immediately trigger the legend rule, sending a card to the graveyard and kicking off Adarkar Valkyrie's resurrection trigger alongside Intruder Alarm's global untap. Because Intruder Alarm untaps Adarkar Valkyrie every single time a creature enters the battlefield, you can endlessly alternate targets between the original creature and Moritte of the Frost to sustain infinite entry, death, and untap triggers.