To get the ability to unlock the Good Ending, you must have a final score of 16,000 (maximum score). If you do not get max score, you will be locked into the Bad End. For the Good End, you'll need 12,900 points by the time you reach the point of no return. (You will be warned of this point of no return before you go in).

To gain the maximum score, you need to:
- Extinguish ALL the red corruption pools around the arcade.
- Find and play the hidden arcade machine (This also unlocks the 4th teddy bear. I do not believe you need all 4 teddy bears, but the other 3 are in very obvious locations, so you shouldn't have a problem with them). It's located in the warehouse, look for a note near a door with caution signs on it (yellow and black stripes). Crouch/go prone near the pinball machine, and go outside. Unscrew the vent, and go through it. You'll find the hidden Janitor machine there. Clean up the blood, and the teddy bear will be right behind you.
- After fighting and defeating the Entity, you need to clean up all the water puddles in the digital world.
- When fighting and defeating the Source, clean up all the red corruption pools, as well as hit and destroy all its glowing yellow weak spots. CLEAN UP THE POOLS FIRST! ONCE ALL WEAK SPOTS ARE DESTROYED, THE BATTLE WILL END! There are 15 pools and 7 yellow spots. Be aware that some of the pools are right next to each other, so count your pools cleansed carefully.

After you defeat the Source, walk through its tunnels as normal, then you should reach its center with Janitor. DO NOT PLAY JANITOR. YOU WILL GET THE BAD ENDING. Instead, destroy all the yellow weak points (Some will be behind the machine). If you do not see the yellow spots, you missed something.

Congratulations, sit back and watch the good ending cutscene.