Laboratory Maniac on the battlefield or in your graveyard or in your library.
Mirror-Mad Phantasm in your graveyard.
The Scarab God on the battlefield.
You have a way to draw a card.
({3} magic symbol) ({U} magic symbol) ({U} magic symbol) ({B} magic symbol) plus an additional ({2} magic symbol) ({U} magic symbol) ({B} magic symbol) available if Laboratory Maniac is not on the battlefield available.
Steps
Activate The Scarab God by paying ({2} magic symbol) ({U} magic symbol) ({B} magic symbol) , exiling Mirror-Mad Phantasm and creating a copy of it, except it's a 4/4 black Zombie.
Activate the Mirror-Mad Phantasm token by paying ({1} magic symbol) ({U} magic symbol) , shuffling it into your library, revealing all cards in your library and putting them into your graveyard.
If Labratory Maniac is not on the battlefield, activate The Scarab God by paying ({2} magic symbol) ({U} magic symbol) ({B} magic symbol) , exiling Laboratory Maniac and creating a copy of it, except it's a 4/4 black Zombie.