A malapropism from Black Adder's buffoon, Baldrick, for 'magnum opus':
Edmund Blackadder.
A giant rollercoaster of a novel in four hundred sizzling chapters. A searing indictment of domestic servitude in the eighteenth century, with some hot gypsies thrown in. My magnum opus, Baldrick. Everybody has one novel in them, and this is mine.
Baldrick.
And this is mine. My 'magnificent octopus'.
-- "Ink and Incapability"
Magnificent Octopus is also the name of an indie prog-rock band.