Adarkar Valkyrie + Intruder Alarm + Dack's Duplicate

Adarkar Valkyrie

Intruder Alarm

Dack's Duplicate

How it works

1. Activate Adarkar Valkyrie by tapping it, targeting any legendary creature you control.
2. Cast Dack's Duplicate 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 Dack's Duplicate.
7. Resolve the Adarkar Valkyrie trigger from step 4, returning the legendary creature to the battlefield from your graveyard.
8. Put Dack's Duplicate 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 Dack's Duplicate to the battlefield from your graveyard as a copy of the legendary creature.
13. Repeat from step 3.

This fascinating loop turns the classic legend rule into a perpetual motion machine by having Adarkar Valkyrie continuously resurrect a shapeshifter while Intruder Alarm untaps her for each new arrival. When you cast Dack's Duplicate to copy a legendary creature you already control, state-based actions send one copy to the graveyard, triggering the Valkyrie while simultaneously seeding the board with untap triggers. As the Valkyrie bounces the original legend and the copy back and forth to the battlefield, Intruder Alarm ensures she stays constantly untapped and ready to repeat the cycle indefinitely.