Sawer is the first boss you encounter, finding him in the Sick area of the apartments after you receive the elevator code from a tape.  As you go down the stairs, you get both glock magazines and morphine syringes, both of which are gonna be crucial in the fight. At the final floor, you just have to walk straight and, before you enter the boss fight, there is a save there. Use it, especially if its your first time. Once you enter the room, its dark, and after a few seconds of silence, a chainsaw goes off. The lights flicker on, revealing Sawer, as skinny and tall as he can get. He'll then run to where you are standing, in an attempt to saw you, but instead saws off your exit-way. Then, you enter the boss fight. It's pretty easy. Run, shoot, once hes down, stab the now-open eye. After a few rounds of that, he succumbs to the pain of decapitates himself, with Simon promptly throwing up, and passing out, possibly in said puddle. That ends chapter 1. Gross. 

You encounter this fat boss in the sewers, in which Dr Purnell just decapitated another human.... because he wanted to know where a key was. Simon interrupts the two, which provokes Dr Purnell to leave and lock the door, before Mace comes into the, might I add water-filled, room and swallows the key. It turns out that the key it swallowed was the key Purnell wanted. To kill this boss, its pretty easy, just turn a few valves, (2 in easy, 3 in medium, 4 in difficult+nightmare), which will power electricity to run through the water. If Simon does not get out of the water in time, he, too, will be electrocuted and die. If Simon is hit by Mace, he will die aswell. Mace hits with the force impact of a car, makes sense... After you kill it, you need to get a saw to get the key. Pretty easy to find in a room opposite Maces body.

Carcass is one of the grossest sounding bosses, a constant gurgling noise coming from him, He is the only boss that you can choose not to fight(Book/Sick Simon do not count, they are ending bosses.)by simply going back the way you came from. It is encountered after Simon and Sophie have a little talk, and she jumps off the roof. Carcass is full-on FORMED by her dead body. It can be killed with a simple glock, around 5 magazines of no to a few misses. Killing it will result in Simon not killing Sophie at the end of the game, but not killing it will result in him killing her at the end, either out of jealously or just pure rage. It is also very hard to dodge, as it tracks your movement. Only way it can attack you is via Hookheads, coming from its stomach. Just kill it, you can get out easier if you do.

To continue on, you must first get the code to the attic door in which Purnell fleed to. It changes depending on whether or not it is a new game, or a loaded game from the previous days.  Once you reach the attic, there will be a ledge with some ammo, a morphine syringe, and a gun.  All of these can be needed, but are optional to grab. Once you walk forward a bit, you should be put into a cutscene, after which the battle will start. Its a simple gunfight, but Purnell can be hard to fully finish off if you do not know what you are doing.  When the battle is over, Simon will walk over to Purnells dead body, and crush his head in, destroying both his skull and mask. If you did not trust him with the gun, you will be given the Taurus revolver. However, if you do trust him, then upon his death you will be given the Ruger P345.

The final battle is a unique one, with special Faceless enemies you have to fight in order to gain four valves. In this battle, you play as Book Simon, instead of Simon, the version you used to play as.  S Simon will use psychokinetic powers to move boards and boxes scattered in the room as he is in a barred off room. If he hits you with these objects, you will take damage. Morphine syringes are still usable, but they are not found in this room. Once you finally get all four valves and spin them into place, the bars enclosing S Simon rise, and you lose control of your character. Book Simon will then, a bit clumsily, will walk over to S Simon and begins beating him up. He eventually knocks S Simon out, and out of his wheelchair, before climbing over him and chokes him to death. With S Simon dead, B Simon collapses too, symbolizing S Simons suicide in the real world. With their deaths, the game ends, and you are brought to the cutscene. The image on the right is B Simon finally ending S Simons life, indicated by the health bar above.

There isn't much to say about this boss, other than that it is much like Sawer. Slowers will help the boss fight the player. Slowers. Plural. There are many slowers that will come.  Its honestly a lot more easier to defeat than all the other bosses.