Adarkar Valkyrie and Intruder Alarm on the battlefield.
Adarkar Valkyrie does not have summoning sickness.
You control at least one legendary creature.
({3} magic symbol) ({U} magic symbol) available.
Steps
Activate Adarkar Valkyrie by tapping it, targeting any legendary creature you control.
Cast Stunt Double by paying ({3} magic symbol) ({U} magic symbol) , choosing to have it enter the battlefield as a copy of the legendary creature targeted in step 1.
Put the legendary creature into your graveyard due to the legend rule.
Adarkar Valkyrie and Intruder Alarm trigger.
Resolve the Intruder Alarm trigger, untapping all creatures.