It is massively larger than before, with a bulkier body and a plethora of new attacks rather than just its original super-chaingun. The Spider Mastermind serves as the final boss of the game, and is implied to be the commander of Hell's forces during the game's events. The Spiderdemon is the second form of the Arachnotron class, and also a boss. She doesn't have a plasma gun, so thank heaven for small favors. The Doom II manual presents the Spider Mastermind as the mother of the Arachnotrons: ' You guess the Arachnotrons had to come from somewhere. Watch for it at the end of the third episode of DOOM, and numerous times times in DOOM II.'

The Official Doom FAQ (included in Doom 1.4) describes the creature as a 'huge robotic chaingun shooting spider,' adding 'it will make you wish you never were playing DOOM in the first place. Perhaps as a result of this, the manual for the Depths of Doom Trilogy erroneously states that it appears in Doom II only.

The Spiderdemon is not mentioned in the Doom manual, presumably to avoid a spoiler.