The Conjurer's appearance is that of a monstrous, humanoid corpse draped in gray, rotten flesh that doesn't quite fit over its body. Its pale and unfitting flesh could also be seen as reminiscent to that of a problematically-developing fetus. It is suspended from the ceiling by chains and long strands of tubing similar to umbilical cords. Only the creature's top half is seen, as the rest of it descends into the blackness surrounding the ring-shaped arena. If viewed closely, black feathers can be seen around its back, a clear connection to the actual corpse of Walter.
This monster is the otherworldly incarnation of Walter Sullivan, created from Walter's own remains. Henry Townshend discovers a normal, human version of these remains in a hidden room behind his apartment shortly after he returns from Room 302 of the Past. Just before the final boss fight, the human corpse inexplicably vanishes.
The Conjurer appears along with Walter's ghost, who looks just like the real Walter before his death, while the third part of Walter's being, Young Walter, is elsewhere. Henry confronts these two parts of Walter Sullivan in a great chamber he finds after descending into a hole below where Walter's corpse secretly resided. During Henry's battle with Walter, Eileen Galvin, in a possessed trance, slowly walks toward an instantaneous death in a huge vat of blood housing a gigantic, revolving, spiked contraption that resembles an armillary sphere. It is in this arena that the final boss battle takes place.
The creature itself doesn't pose a threat to Henry during the battle, merely moving its head about and emitting very deep, bellowing sounds. As long as the Conjurer remains intact, Walter's Ghost, the true threat, will be invulnerable to attack. When Henry uses Walter's original umbilical cord on the creature, it cries out, apparently forcing Walter to recall past trauma discovered earlier. This unlocks the eight Spears of the Holy Mother surrounding the arena, each of which is embedded into a silhouette of one of Walter's victims.
Each spear must be collected and jabbed into the creature (it is suggested that Henry go into battle with at least four item slots free). When all eight spears are used, the creature cries out again and goes limp, rendering Walter's Ghost mortal and able to be slain.
Walter fights as he does in his Ghost appearances, wielding a pipe and a handgun, both of which are fairly dangerous. He can also take a great deal of damage, much more than any other ghost or enemy in the game. When Walter finally dies, the Conjurer roars in pain and Walter himself passes away, begging for his mother one last time. Young Walter fades as well, along with the Conjurer.
The Conjurer represents a facet of Walter's soul and being, as well as his desires and state. The Conjurer is nestled deep within the Otherworld of Room 302, which Walter believes to be his mother. As such, the Conjurer is symbolic of Walter returning to his "mother's" womb. It also shows Walter's "monstrous" nature, as opposed to Young Walter, who displays Walter's former self and good innocent qualities.