Would ask for this to be stickied, or deleted if for some reason no one likes it.
Portal, based on the half-life 2 engine, is one of the greatest games of this generation, and many would argue of all time. The game is fun, challenging, and can be played for long hours at a time. The games uniqueness brings about a number of glitches that are used by both speed runners and casual players alike.
I'm putting this list in order of ease of use, and I'll include demos in chambers from the original game.
**Portal Bumping:** Portal bumping is probably one the most useful of all portal glitches, as it has a tendency to be over looked by map makers. Portal bumping is when you use a portal placed on a surface, to force a second portal through an otherwise un-passable object or surface.
**Portal Standing:** Portal standing is another very simple technique that you might have never realized you used! Portal standing, simply put, is when you shoot a new portal while standing in the old one. Crouching actually makes this a lot easier (I find) because you move less while crouching. Again, check out the demo if your unsure what I'm talking about.
**Portal Peeking:** This is a quite a bit like standing, except instead you use an already placed portal to shoot the next one, without actually being where you were...that's one hell of a sentence. You would use this technique if you want to have a portal between two places that you can't physically see.
**Accelerated Back Hopping (ABH):** This is a very common speed running technique that comes from the HL2 engine. You achieve ABH by bunny hopping backwards, some people claim you need to do a 180 in the air, but this is not the case. When you ABH, you don't hold backwards (S in most cases), and the bunny hopping aspect comes from either a script or manual input.
**Item Climbing:** This one is hard to explain, but in essence, it stems from the fact that you can stand on items. It's achieved by standing on an item, jumping, while in the air, grabbing the item (so it comes up to your feet), jumping off of it again, and repeating. Scripts are very commonly used for this feat.
**Edge Glitching:** Edge glitching is another example of forcing yourself places. Instead of portals, this time were forcing ourselves places. Basically, you have the edge of a portal up against a wall, and the equivalent edge of the other portal on an edge. You approach the second portal from the side, and you have the ability to shoot a portal into the room...or lack there of on the other side.
REALLLY STUPID GLITCH
To use this glitch, you need to go to the console and type 'kill'. You will instantly win the game. ~By Pestchamber
Demos: They are named for what they represent.
http://files.filefront.com/13758574
http://www.megaupload.com/?d=4PFC6Y7Z
I didn't include info nor demos on OOB nor the Save/Load perspective glitch (since I frankly don't know how the save/load glitch works, and this site has a hatred of OOB). I will add though, that youtube is your best bet for either of them.
[Updated with a new mirror]


