Activate Altar of Dementia by sacrificing Iridescent Drake.
When Iridescent Drake dies, Minion's Return triggers, returning Iridescent Drake from your graveyard to the battlefield.
When Iridescent Drake enters the battlefield, it triggers, returning Minion's Return from your graveyard to the battlefield attached to Iridescent Drake.
Resolve the Altar of Dementia ability from step 1, causing target player to mill cards equal to Iridescent Drake's power.