Adarkar Valkyrie + Intruder Alarm + Vesuvan Shapeshifter

Adarkar Valkyrie

Intruder Alarm

Vesuvan Shapeshifter

How it works

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

This fascinating loop relies on Vesuvan Shapeshifter entering the battlefield as a copy of a legendary creature you already control, instantly sending one copy to the graveyard via the legend rule to trigger Adarkar Valkyrie's delayed return ability. Meanwhile, Intruder Alarm acts as the engine's heartbeat, turning every entry into a cascade of untaps that continuously refreshes Adarkar Valkyrie's tap ability. By ping-ponging the resurrection target back and forth between the Shapeshifter and your original legend, you sustain an endless cycle of deaths, enters-the-battlefield triggers, and untaps.