Instant Air Special (abbreviated to IAS) is the act of doing an air special attack immediately after jumping. Also sometimes known as Tiger Knee, although the two are not the same strictly speaking.
The idea is to:
- buffer the motion for the special attack while on the ground
- input jump after the motion
- once airborne, immediately press the button
This can be applied to any air special/super attack and allows players to do an air special almost as if there were a ground version!
Tiger Knee
Tiger Knee (abbreviated to TK) is the name of Sagat's move in the original Street Fighter 2, which was 
.
Unlike most IAS moves in modern games, Sagat's Tiger Knee is a ground special, and does not work in the air. So one needs to press the final button before the jump, doing otherwise results in a regular jump kick.
In the subsequent games (and SF2 re-releases) the Tiger Knee input was changed to 
instead, so it's no longer a "Tiger Knee" input, so to say.
The difference between the terms "TK" and "IAS" is that "TK" primary focuses on the input (and usually covers any motion input ending in 
, 
or ), whereas "IAS" on the resulting move (regardless of how the move is inputed).
Examples
- GGXRD-R2
- Baiken's Youzansen
GuardHigh/AirStartup6Recovery14+ 6 after LandingAdvantage-17 (
). Inputted as ~
- Youzansen is an overhead, and gives Baiken access to a fast overhead attack
- I-No's Ultimate Fortissimo
GuardMidStartup7+0Recovery16Advantage- (air 
). Inputted as ~
- Ultimate Fortissimo grants a lot of frame advantage on block, thus allowing I-No more time to do mixups
- BBCF
- Nu's Crescent Saber (
). Inputted as ~
- Crescent Saber is an overhead, and greatly improves Nu's mixup game.
In these examples the goal is to input a jump after inputting the motion for the special move, then press the button shortly after.
However IAS is applicable not only to motion inputs. For example:
- DNFD
- Inquisitor's IAS j.M
GuardMidStartup12Recovery26Advantage-1 (
) does not involve any input tricks and is a plain ~ when starting from the ground
- j.M is a giant low crush that is safe on block
- GGST
- Similarly, Jack-O's j.D (
) with held servant is ~
- j.D launches the servant in a low arc different from the grounded 5D version
Minimum Height
Some air attacks require that you be at least a certain height off the ground before the attack can be used (referred to as minimum height). A common example of this is Ky's Air Stun Edge. In cases like this, you will need to delay your button press so you can gain more altitude first.
Inputting the Jump
It should be noted that the jump motion doesn't have to be inputted at the end of the move! For example, to TK a 
motion, you can do !
Prejump Cancel
A Prejump Cancel is canceling the grounded startup animation of a jump into a ground special attack. While not exactly the same as a Tiger Knee, this can be done using the same motion with slight differences - you need to time the button press to to happen during the jump's ground startup, which is a much smaller window of time compared to normal TK attacks.
An example of this is Susano'o Dancing Dual Kick (
). The final hit is jump cancelable, which can let you cancel into ground special moves by using this technique. So to cancel into a second Dancing Dual Kick, do right when the final hit of the first one happens, then press during the jump startup. Another way to do this is to input a jump as the attack connects, then the motion i.e. .