Hyperspeed Jump Kicking
Hyperspeed Jump Kicking (HSJK) is a hyperspeed technique where Mario builds up speed by jump kicking repeatedly on a suitable steep slope.
In order to perform HSJK, Mario must jump kick and land on a low friction floor, usually with some means of holding him in place. The properties of the slope required for HSJK are the same as for Hyperspeed Grinding, as both involve the same landing action. However, the conditions required to hold Mario in place during HSJK are more closely related to those for Backwards Long Jumping than to those for Hyperspeed Grinding. This is because each jump kick gives Mario positive vertical speed, whereas grinding has strictly non-positive speed. Many HSJK methods require that the landing accelerates Mario, in addition to providing no friction due to the lack of air acceleration. This imposes additional restrictions on the kinds of slopes that can be used, but also makes HSJK usable for building up backwards speed in addition to forwards speed.
The first method of HSJK to be discovered, Corner HSJK involves repeatedly jump kicking into the corner between two walls such that Mario is facing the unreferenced one. This method can theoretically build up to a maximum of roughly ~400 speed before breaking free. It is the only method in which Mario spends significant time in the air, and as a consequence it cannot build up backwards speed.
Low Ceiling HSJK
The other basic form of HSJK, Low Ceiling HSJK involves using a Pedro spot to hold Mario in place. This method only allows for at most two air acceleration frames per jump kick, and thus requires the floor to accelerate Mario during his landing frames. The speed that can be obtained this way is limited by the size of the Pedro spot.
If a floor is steep enough that Mario can slide on it with landing animation to gain sufficiently large speed, then Mario can HSJK on that slope backwards, counteracting the fact he would lose 0.85 speed for every air frame. Hypothesized by Sidney, but it is likely possible given ideal geometry.