Adarkar Valkyrie + Intruder Alarm + Sakashima's Student

Adarkar Valkyrie

Intruder Alarm

Sakashima's Student

How it works

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

This brilliant loop turns the legend rule into an engine, using Sakashima's Student to repeatedly copy a chosen legendary creature and immediately sacrifice itself to the state-based action. Adarkar Valkyrie steps in to catch whichever copy just hit the graveyard, returning it to the battlefield so it can enter anew and trigger Intruder Alarm's static ability. Because Intruder Alarm untaps all creatures every time a new creature enters, Adarkar Valkyrie stays refreshed and ready to tap for the next cycle, generating an endless stream of entries, leaves, and untaps.