You control a permanent that can tap to produce at least ({U} magic symbol) .
Steps
Activate Altar of Dementia by sacrificing Coral Trickster.
When Coral Trickster dies, Missy's first ability triggers, returning Coral Trickster from your graveyard to the battlefield face down as a 2/2 Cyberman artifact creature.
Resolve the Altar of Dementia ability, causing target player to mill cards equal to Coral Trickster's power.
Activate a mana-producing permanent by tapping it, adding at least ({U} magic symbol) .
Activate Coral Trickster's morph ability by paying ({U} magic symbol) , turning it face up.