Infinite Health Door

Infinite Health Door is a glitch that allows the player to get an infinite amount of health. The glitch is caused by a mapping error, and can only be performed in the map c2a5f.

This trick is very useful for the rest of the game while speedrunning, since you can do virtually unlimited damage boosts or take other damage and survive.

Explanation

For some reason, all the doors in the map have a damage value of -1, meaning that the game will HURT you with -1 damage (being a double-negative this means you gain health) per tick (or frame).

Since the HEV (armor) reduces the damage you take at 5 regular points => 2 HEV and 1 HP and uses rounding for values less than 5, 1 regular point lost with HEV becomes 1 HEV and 0 HP lost. Thus you must have zero HEV otherwise HEV will increase and health will remain the same. The value is a 32bit integer so that means a maximum of 2147483647hp. To reach that value, you'd have to stand in the health door for 24 days (576 hours).

Raising the FPS can speed up the healing rate as you get n amount of hp per second related to your FPS. So 20fps is 20hp/s, 1000fps is 1000hp/s and so on..

Properties of one of the doors present in the map, showing that the damage value is set to "-1".

Instructions

To trigger the glitch, you have to get stuck in one of the doors of the map. This can be done in multiple ways: either by standing behind the door so that it crushes you, or getting stuck in the seam while it's opening up.