Adarkar Valkyrie + Intruder Alarm + Phyrexian Altar

Adarkar Valkyrie

Intruder Alarm

Phyrexian Altar

How it works

1. Activate Adarkar Valkyrie by tapping it, targeting another nontoken creature you control.
2. Activate Phyrexian Altar by sacrificing the creature targeted in step 1, adding one mana of any color.
3. When the creature dies, Adarkar Valkyrie triggers, returning the sacrificed creature from your graveyard to the battlefield.
4. When the creature enters the battlefield, Intruder Alarm triggers, untapping all creatures.
5. Repeat.

This clever loop spins entirely around Adarkar Valkyrie's delayed trigger, which marks a creature to return when it dies, allowing you to feed that creature directly to Phyrexian Altar for any color of mana. Because Intruder Alarm keeps creatures permanently locked down during normal untap steps, its real power is the global untap triggered every single time a creature enters the battlefield—which happens automatically the moment Adarkar Valkyrie's effect resolves and returns your sacrificed creature. By cycling the target creature back and forth between the graveyard and the battlefield, Intruder Alarm untaps Adarkar Valkyrie (and any other creatures you control) along the way, generating an endless cascade of colored mana and death triggers.