You have at least one artifact creature card in hand.
You have at least one artifact creature card in your graveyard.
({B} magic symbol) available.
Steps
Activate Tortured Existence by paying ({B} magic symbol) and discarding an artifact creature card, returning another artifact creature card from your graveyard to your hand.
Imotekh triggers, creating two 2/2 Necron Warrior artifact creature tokens.
Activate Altar of Dementia by sacrificing a Necron Warrior.
When the Necron Warrior dies, Pitiless Plunderer triggers, creating a Treasure artifact token.
Resolve the Altar of Dementia ability, causing target player to mill cards equal to the Necron Warrior's power.
Activate the Treasure by tapping and sacrificing it, adding ({B} magic symbol) .