One of the things that new SF players take for granted is that an input will result in the same thing happening every time. This isn't an unreasonable assumption most of the time - if you input throw, you want to get a throw every time, and most of the time you will. However, occasionally there will be some ambiguity in how the game engine interprets inputs based on your interaction with opponents, and this can result in one input giving different results in different situations. Inputs that can give two different results based on in-game character interaction are known as option selects.
Let's examine some of the most common option selects in 3rd Strike, and what makes them useful:
Crouching throw tech - d. + LP + LK
Earlier, I mentioned ambiguity in how the game interprets certain inputs; one such example includes the throw input while crouching. The 3rd Strike engine doesn't allow you to throw someone else while crouching - try inputting d. + LP + LK to verify this if you like. However, it does allow you to throw tech while crouching, with the exact same input. There, the d. + LP + LK input has two different results based on what your opponent does:
Opponent tries to throw you: you get a throw tech.
Opponent doesn't try to throw you: you get a cr. LP. This is because LP has priority over LK if both buttons are pressed and throw can't come out for reasons like the one listed above, that you can't throw while crouching.
It should immediately because obvious why this is a useful option select - instead of potentially whiffing a throw in the second scenario, which is often what your opponent is trying to bait you into doing for an easy punish, you get a fast low poke that can interrupt your opponent's rushdown. Instead of just covering a throw tech with a standing throw, you also cover other options like tick throws, hesitation moves, etc. This is why crouching when going for a defensive throw tech is often recommended.
Of course, there are still vulnerabilities to this option select - no offensive or defensive option is ever foolproof. If you use this too frequently, your opponent can simply bait it and parry the low jab or space themselves in a manner that allows them to punish it with a move that outranges your low jab. You can always mix things up by throwing in regular standing throws, which will punish parry fishing, or simply jump to escape throws and many other offensive pressure chains. The key, as always, is to avoid falling into easily identifiable or punishable patterns.
SGGK - high/low parry, followed immediately by kara-throw
Another ambiguous situation arises when parries are combined with kara-throws. Typically, kara-throws involve cancelling a normal into a throw so quickly that the initial move doesn't connect. However, after a successful parry, the 3S engine only considers the next valid input to determine what comes out. In the case of a kara-throw, the next valid input is the move with which the throw was kara-canceled, so instead of getting a kara-throw you get the move with which you kara-canceled it.
By far the most well-known example occurs with Chun-Li's kara-throw with close st. HK. Ordinarily, one would use far st. MK to kara-throw, as it gives considerably more range. However, after a successful parry, close st. HK is a far more useful move than st. MK, as it can be comboed into SA II. Therefore, the idea with st. HK xx LP + LK is as follows:
No successful parry: Kara-throw comes out.
Successful parry: close st. HK comes out, which is comboed into SA II if you have meter.
Again, this puts your opponent in a difficult position - going for a throw tech is risky because she can simply step out of range and do a standard SA II combo, but throwing out fast low pokes like cr. LP or cr. MK is also risky because she can parry into st. HK with SGGK. Incidentally, this is an excellent counter to the previous option select, since both possible results are either neutral (throw tech) or in Chun-Li's favor (parry low jab, st HK xx SA II).
Below is an example of the SGGK option select in action (occurs at 0:39, 1:57, and 3:30):
Let's examine some of the most common option selects in 3rd Strike, and what makes them useful:
Crouching throw tech - d. + LP + LK
Earlier, I mentioned ambiguity in how the game interprets certain inputs; one such example includes the throw input while crouching. The 3rd Strike engine doesn't allow you to throw someone else while crouching - try inputting d. + LP + LK to verify this if you like. However, it does allow you to throw tech while crouching, with the exact same input. There, the d. + LP + LK input has two different results based on what your opponent does:
Opponent tries to throw you: you get a throw tech.
Opponent doesn't try to throw you: you get a cr. LP. This is because LP has priority over LK if both buttons are pressed and throw can't come out for reasons like the one listed above, that you can't throw while crouching.
It should immediately because obvious why this is a useful option select - instead of potentially whiffing a throw in the second scenario, which is often what your opponent is trying to bait you into doing for an easy punish, you get a fast low poke that can interrupt your opponent's rushdown. Instead of just covering a throw tech with a standing throw, you also cover other options like tick throws, hesitation moves, etc. This is why crouching when going for a defensive throw tech is often recommended.
Of course, there are still vulnerabilities to this option select - no offensive or defensive option is ever foolproof. If you use this too frequently, your opponent can simply bait it and parry the low jab or space themselves in a manner that allows them to punish it with a move that outranges your low jab. You can always mix things up by throwing in regular standing throws, which will punish parry fishing, or simply jump to escape throws and many other offensive pressure chains. The key, as always, is to avoid falling into easily identifiable or punishable patterns.
SGGK - high/low parry, followed immediately by kara-throw
Another ambiguous situation arises when parries are combined with kara-throws. Typically, kara-throws involve cancelling a normal into a throw so quickly that the initial move doesn't connect. However, after a successful parry, the 3S engine only considers the next valid input to determine what comes out. In the case of a kara-throw, the next valid input is the move with which the throw was kara-canceled, so instead of getting a kara-throw you get the move with which you kara-canceled it.
By far the most well-known example occurs with Chun-Li's kara-throw with close st. HK. Ordinarily, one would use far st. MK to kara-throw, as it gives considerably more range. However, after a successful parry, close st. HK is a far more useful move than st. MK, as it can be comboed into SA II. Therefore, the idea with st. HK xx LP + LK is as follows:
No successful parry: Kara-throw comes out.
Successful parry: close st. HK comes out, which is comboed into SA II if you have meter.
Again, this puts your opponent in a difficult position - going for a throw tech is risky because she can simply step out of range and do a standard SA II combo, but throwing out fast low pokes like cr. LP or cr. MK is also risky because she can parry into st. HK with SGGK. Incidentally, this is an excellent counter to the previous option select, since both possible results are either neutral (throw tech) or in Chun-Li's favor (parry low jab, st HK xx SA II).
Below is an example of the SGGK option select in action (occurs at 0:39, 1:57, and 3:30):
D.E.D - meter based option select
Thus far the option select discussed are possible due to ambiguity in how the game interprets your inputs - a kara-throw not being interpreted as such, for example. However, there are also option selects that don't rely on quirks of the 3S engine, just on basic mechanics such as how meter works, and the fact that you get more meter for a move that connects than one that is blocked. This option select only works if don't have a full meter yet, but are reasonably close (~70-90% depending on the normal used for the option select, and the size of the meter).
To explain the D.E.D option select, I'll use a hypothetical situation and some made-up numbers. Say you're playing Chun-li, and you're currently at 85% meter. A blocked b. + HP gives ~10% meter, whereas a b. + HP that connects gives ~20% meter. (These numbers are probably not accurate, but bear with me). What happens if you do back fierce into super without confirming in this situation?
Back fierce is blocked: You're at 95% meter when you attempt to super, so nothing happens. All you get is a blocked b. + HP.
Back fierce whiffs/gets parried: You're at 85% meter when you attempt to super, same as where you started, so nothing else happens.
Back fierce hits: You're at 105% meter when you attempt to super, so the super comes out, and it combos because b. + HP connected.
The end result in this situation is that super only comes out if back fierce actually connects, so there's no need to confirm it in the first place. You can just bang it out without confirming and be perfectly safe in doing so. This is a particularly nice option select because there's no real down side to it - you might get parried, but then it's not any worse than just having a normal parried in any other situation, at least you don't waste a meter in the process.
Now, although it's nice to just be able to do something like back fierce xx super without confirming, you could always just confirm it too, so that's not where the real value lies. The reason this is so good is because you can use it to do combos that would normally be unverifiable, like cr. LK xx SA III or close st. HP xx SA III, both with Ken. Ordinarily close st. HP is an unverifiable normal, and you'd need two cr. LK's to confirm the combo into super, but if you're paying close attention to your meter, then you can just throw these out safely. You gain range on both of these D.E.D option selects since you'd need to be closer to combo two cr. LKs than just one, and to do the MP, HP target combo instead of just HP.
Here is an example of D.E.D in action. Ken does the normally unverifiable cr. LK xx SA III combo by taking advantage of D.E.D (occurs at 24:56):
Option selects are crucial to becoming a better, more consistent player, and mastering them will help you out in every aspect of your game.