Adarkar Valkyrie + Intruder Alarm + Phyrexian Metamorph

Adarkar Valkyrie

Intruder Alarm

Phyrexian Metamorph

How it works

1. Activate Adarkar Valkyrie by tapping it, targeting any legendary creature you control.
2. Cast Phyrexian Metamorph by paying 3U/P, 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 Phyrexian Metamorph.
7. Resolve the Adarkar Valkyrie trigger from step 4, returning the legendary creature to the battlefield from your graveyard.
8. Put Phyrexian Metamorph 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 Phyrexian Metamorph to the battlefield from your graveyard as a copy of the legendary creature.
13. Repeat from step 3.

This clever loop turns the legend rule into an engine for infinite value, anchored by Adarkar Valkyrie's tap ability to rescue dying creatures. By using Phyrexian Metamorph as a flexible copy of a legendary creature, you can intentionally trigger the legend rule to send the copy to the graveyard while Adarkar Valkyrie's delayed trigger waits to bring it back. Meanwhile, Intruder Alarm acts as the crucial catalyst, ensuring that every creature's entry untaps Adarkar Valkyrie so she can immediately target the next piece to repeat the cycle.