The final boss of Cry of Fear in endings 1, 2 and 3. These are attainable if the player chooses to escapeCarcass, refuses to give the P345 to Doctor Purnell, or both. He is the manifestation of the 'real' Simon, who was crippled by the impact of the hit and run incident at the beginning of the game. Under the instruction of Purnell, he began to write a book about his emotions that gave birth to the world depicted in the game- a depiction of Simon struggling with his inner emotions. In reality, the Simon you play as is merely a depiction of him in the real Simon's head.
After finishing writing the book in ending 1,2 and 3 ; Simon shoots himself in the head and Book Simon (the protagonist) is sent into a nightmare world (his own head); the realm bloodied and constantly changing, with countless book pages with "Suicide" written on it. Book Simon will proceed to make his way through the warped world and eventually climb to where Sick Simon resides- a depiction of what is left of the real Simon, attempting to fight away his evil twin. It can be presumed that the fight itself is a depiction of Simon's actions eventually overwhelming him, driving him to commit suicide.
The fight against Sick Simon is possible, but potentially difficult for those who do not know what to do. Simon will sit out of reach behind several steel bars, gunshots having no effect on him. Simon will use psychokinetic powers to throw items at the player, forcing them to time their jumps and crouches just right to avoid them. The player will also have to fight four hordes of unique Faceless, one of the creatures within the horde being a 'Twisterv' variant, causing it to drop a Valve upon death. All four valves can then be used in separate corners to raise the bars blocking the player from reaching Simon.
Upon finally raising the bars, Book Simon will enter the room and proceed to mercilessly beat the real Simon unconscious before strangling him to death. The death of Sick Simon results in Book Simon collapsing as well, the conclusion of the battle causing the real Simon to give in and commit suicide. In ending 4 of the game, Sick Simon is a playable character.
Ending 4 is achieved by killing Carcass and giving Purnell the gun he requests. In this ending, Simon is subjected to another hallucination where he is preparing to commit suicide before Book Simon enters the room. Having come to terms with all his inner demons in this ending, the real Simon no longer needs his evil counterpart who served as his weapon against his nightmares- thus he sets out to kill it in an alternate final boss fight. This results in the death of Book Simon and the 'good' ending of the game where Simon lives.
Simon's wheelchair is actually a recycled portion of the Wheelchair Twitcher's model from Afraid of Monsters. The two models also share the exact same textures for the wheelchair.
While strangling Simon, you as well as Simon will lose health.