Reportal
A reportal is a trick that allows you to gain more exit velocity when going through a portal. This is used in a few places in the glitchless category, like chamber 14, high level chamber 15, and intermediate to high level chamber 18. It is also used in other categories in a few places.
How To
Replace the opposite color portal that you are currently in. Note that shooting the wrong portal will trigger FCPS which will not give velocity, but this is used in various Out of Bounds reentries.
The video below gives a demonstration and on screen instructions.
Details
Reportals only work on players and only when a portal is moved (i.e. not fizzled), no attempt is made to add velocity to other entities. Exactly 100 velocity is applied to the player in the direction of the portal normal, bypassing the normal maximum portal exit velocity (1000 units in any direction). (github leak link)