This page contains spoilers for the ending of the game. If you plan on playing the game spoiler-free, don't read past this point.
At the end of the game, after choosing to go through The Last Area instead of leaving the sewers, the player finds themselves in a hallway that progressively fades to white. After the game fades back in, the player will find themselves at a regular sewer exit. Upon climbing out, they will find their dog outside the sewers. The screen then fades again, showing the ending splash screen;
"Just leave" Ending
At the very start of the game, if you spam the E key while climbing on the ladder you will get this ending;
Escape Without Your Dog
At the end of the game, after choosing the sewer exit and not The Last Area, the player simply leaves the sewers without their dog. The game then fades to this splash screen;
Dead Dog Ending
In the Sewers, the player can attempt to shoot the shadow of the dog that appears at the end of the second section. After doing so, the player will be sent to a sewer exit.
However, once you have left the sewer the player's dog lies on the ground, telling you negative things when interacted with. After spending a rather long time in this area, the screen then fades to white. Finally, it fades to a splash screen;
This ending is arguably the hardest to achieve, as it requires extra steps to be taken.
Secondly, in The Sirens Lair, after killing The Siren the player must leave the area and then return to retrieve a Child's Skull from the Siren's corpse.
Lastly, the player must place the Child's Skull in what looks like a tree stump in The Last Area, just past the Goobles.
Then, once you leave the sewers, the player will be introduced to a new ending area. The city is filled with screams and sirens, the sun is completely blocked out, and everything has a red tint. The game then fades to a splash screen;
At the end of the sewers where you would normally get the handgun in the full game, you are prompted with three options.
If "Pizza, pizza, and pizza" is picked, the player is transported to a hallway that uses textures from Spooky's Jumpscare Mansion. The Eyeless Hobo will chase you with a slice of pizza and attempt to kill you with it.
The goal in this ending is to run to the end of the hallway, pick up a slice of pizza, and then run back without dying to the pizza-wielding hobo. This section ends with a full image of the pizza poster from Spooky's Jumpscare Mansion that says "You Win!"