Next to game breaking bugs and annoying bugs, games like half life have interesting bugs that actually add to game enjoyment.
Like for example:
1. Bunny hop - Where you press jump at the exactly right moment to increase speed of movement.
2. Air accelerate - Where you can magically move in the air, and where there is low gravity accelerate very fast with the use of air movement and/or bunny hop. Some counter strike servers have Biohazard zombie mod where you have an parachute that makes you float in the air a bit. Using this and various kinds of speed boosts you can perform some neat flying.
3. Long jump - Using air accelerate movement, aka jumping and quickly doing strafes in the air (a strafe is pressing an direction button and moving the mouse pointer into that direction, than after a certain length back to the opposite side : A + Mouse left => B + Mouse right , as much as possible during the jump) the player can achieve jumps over normal boundaries, aka running and simply jumping. Maximum jump with out air control is 215 game units. With extremely tricky long jumps player can reach up to 272 units, or maybe more. But this requires 8 strafes during a single jump, and that seems almost impossible. There are a few types of long jump that include different jump preparation techniques.
4. Surfing - Any tilted surface to a certain angle will allow player to glide on it. The player ca jump onto an angled surface and simply hold one of the direction keys ( For example, the object is on the left of the player, the player will jump and press A button, aka command to strafe left, and than proceed to move his mouse in an precise order in order to perform surf) to move forward (or if skilled enough even backward).
5. Wall bug - Only performed on angled walls, allows player to stop it self instantly when falling. The player has to be very close to the angled wall he is falling from, and by looking at an certain direction and pressing certain keys, the player can stop him self from falling instantly, and wont take fall damage no matter how hight he fell.
6. Jump bug - The player can jump from any height what so ever and take no fall damage on any surface (except trigger hurt of course). This is done by jumping and pressing DUCK in the air, than when the player is falling he must release duck at PRECISELY 4 units (or less) before hitting the ground, and than jump. The game will think he simply jumped and will ignore all fall damage. 4 units are 3 inches in length ( or 7.62 cm).
There are various bugs on moving surfaces such as trigger push or func conveyor, where a player would bing the DUCK command onto his scroll wheel (because scroll wheel can rapidly send commands when used), and while in any of the two environments the player can scroll, aka duck rapidly, and accelerate him self instantly to speeds above normal. Besides ducking the player can also use air control and bunny hopping.
Water for example neutralizes fall damage, unless the water height is 1 units.
Many mods exist upon these bugs and are fun to play.
As for classic HL single player, a lot of bugs that affect NPCs can happen. Some times in some scenes the game is so broken its not funny (HL from 1998, not updated). Some times the scientists bug out and die on their own on moving objects such as doors. And some times when they die their body stays and they constantly twitch and some times say words repeatedly.
I remember the crab monster from Xen not dyeing after i pretty much shoot everything into its ugly self. Than again at the same level you don't even have to fight it at the final stage, you can simply blow the hole up with explosive charges. It will die instantly shortly after that.
Grenades can be abused to gain speed and bunny hop in single player HL. Bunny hopping is much more easy in HL than in CS.
A nice bug is if you have an audio CD inside your CD tray, the game will play songs off of that CD when you are in the process of loading an another map. CS has this same thing.
Due to uneven geometry, aka tilted faces and sharp angles, the player can get stuck in the wall.
Also half life texture/face sub divide is set to 240 units, 256 can, and almost always crashes the map.
There is a whole lot technical stuff too. I cant remember much distinctive single player bugs, i played HL SP a long time ago last time. But i do know a lot of engine bugs 😀
I don't even want to mention James Bond night fire 🤣
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