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Excursion Funnel Flying
Excursion Funnel Flying, or ExFu for short, is a glitch in Portal 2. This occurs due to the game engine assigning a flying tag to the player while being in an Excursion Funnel, and the player manipulating the game engine to keep the flying tag while outside of the Funnel, effectively flying.
Entering flying mode
Start by walking or falling into a funnel. Wait until you reach the top of the funnel, and watch your velocity from the cl_showpos command. When that zeros out, change your crouch state (if you were crouched, uncrouch and vice versa). Stay in whatever your new crouch state is and exit the funnel by moving out of the funnel normally using your directional keys or air-strafe out to exit with extra speed. You will now be moving in a zero gravity state until you either reenter the funnel, remove a portal that you manipulated the funnel with or change your crouch state. However, if you make a save while in zero gravity and load back to that save, you can crouch and uncrouch freely without removing the glitch.
Be sure when attempting this glitch you never jump into the funnel, as this will render you unable to crouch, a vital part in getting this to work. It's also recomended to have cl_showpos 1 enabled in the console to know exactly when you stop moving.
Movement while flying
You can move around while in no gravity by doing air-strafes. Note that the speed cap of 300 UPS is still present, so you will lose all air control if you go over that threshold. This is why it is recommended to keep your speed under control because once you lose air control, the only thing that can stop you is a wall or a barrier.
If you want to descend or ascend, try and find a sloped surface facing up or down and fly into it.
If you manage to land on the ground, provided that you don't change your crouching state, you can move around freely on the ground and any surfaces that are ≤18 units higher or lower than the ground. If you try to walk down onto a surface that is >18 units lower than the ground, you will float off from the ground at the same height as the ground you walked off; if you jump you will float up at the speed and direction that you jumped up from.
- This glitch is also known as the Crouch Flying Glitch or CFG.
- If you do this glitch while in a funnel that was not manipulated by a portal of yours, it's possible to take the glitch with you past level changes.
DemonStrate, ExplodingCabbage, Inexistence and Scepheo for their research on this glitch. More information can be found here