[Edit: Bah, I've just written a novel for nothing...]
SXS means that you don't finish a combo, and instead, Xianghua says "Just kidding!"
When you do this, you can follow up with an attack.
First there's SXS 1. You can follow up with attacks. The possible attacks are A, or B, or K.
On playstation, that's probably square, triangle, and circle...
Second, there's SXS2, which is the same as SXS1, except that you can follow up with a grab if you want, or a taunt, if you want. The attacks are still available, but the same as SXS1.
SXS3, the grab is the same, the taunt differs, and the attacks get an additionnal effect attached to them.
Well, let's say that you perform [A+K] (Hold) ... She spins on the ground, and then says "Just kidding!"
You've performed SXS level 1, and accumulated one stock.
You do it again. [A+K], she spins, says "Just kidding!"
You've performed SXS level 1, and accumulated a second stock.
You do it a third time, you've performed SXS level 2, and accumulated a third stock.
It means that when you have 3 stocks, you start doing SXS level 2.
You do it a fourth time, level 2, stock 4.
You do it a fifth time, she flashes blue.
It means that you've entered SXS3. (Level 3, Stock 5.)
That's the maximum level.
Now, let's reset. (Click on the right hand joystick, or choose the reset option in the option menu.)
You're back to square one.
Hold A+K 5 times. On the fifth time, after she says "Just kidding!" and makes a blue flash, press K.
Now hold A+K once again. You'll notice that she's not flashing anymore.
That's because the K attack has costed 3 stocks.
5 stocks minus 3 stocks = 2 stocks. Because of the [A+K] you just did, you now have 3 stocks. You need to do it two more times if you want to go back to 5 stocks, which is level 3.
So, 3 stocks is SXS2, 5 stocks is SXS3, and you can go up to 8 stocks, that's the limit.
If you follow SXS2 or SXS3 with a taunt, it raises your stocks even more than just sitting there, waiting for the SXS animation to finish.
Each attack that chains from SXS costs a set amount of stocks.
Your amount of stock remains after a round, so if you win a round, it's good to hold [A+K] to get more stocks ready for the next round.
The additionnal effects attached to SXS3 attacks are clearly written in X_A's post.
And if you didn't get that already, I use [A+K] in my example because it's one of the attacks that lead to Xianghua saying "Just kidding!". So you can replace [A+K] with whichever attack that you want which leads to SXS. The list of those attacks is also clearly written in X_A's post.
