You control another nontoken nonartifact creature.
Steps
Activate Altar of Dementia by sacrificing another nontoken nonartifact creature When the creature dies, Missy's first ability triggers, returning the creature from your graveyard to the battlefield face down as a 2/2 Cyberman artifact creature.
When the creature enters the battlefield, Intruder Alarm triggers, untapping all creatures.
Resolve the Altar of Dementia ability from step 1, causing target player to mill cards equal to the sacrificed creature's power.
Activate Skirk Alarmist by tapping it, turning the creature face up.