Well, first off, I'm done with uni for the year, FINALLY. :D
So, a lot of people see X-23 as basically Wolverine-lite. Anything X-23 can do, Wolverine can do, better. He's got more health, supposedly better damage for much easier execution, and in some areas, better normals and has an overhead. There's not point picking her, she'd mediocre, not very threatening and doesn't do well in tournaments usually. That's kinda the popular view anyway.
In my opinion, X-23 isn't another version of Wolverine. She's her own character and she operates differently from him, though they're both offensive characters. Mirage Feint commonly gets compared to Berserker Slash, because both moves cross-up and are used to create left and right mix-ups. People just straight-up see Mirage Feint as a much weaker Berserker Slash because it has no invincibility, leaves her open and isn't an attacking move, therefore, it can't be used to get in effectively. The thing is, Mirage Feint isn't really supposed to be used as a tool to get in, at least not without assists anyway. Mirage Feint is used, like mentioned before, to create left and right mix-ups. It's also used to push against advancing guard and keep yourself in in their face when pushed back. It's used in combos. It's used to cancel your normals(more on this later) and it's used for mix-ups on character's wake-up. Mirage Feint has a lot of indirect uses something only one X-23 player so far is making any use of. IMO, the key to mastering X-23, lies in mastering Mirage Feint.
X-23 thrives on assists. She needs assists to help her land her Weapon X Prime hyper, a key move in helping her create the DHC trick/glitch to reset damage. Assists give her cover and boost her offensive game greatly. Some people think X-23 is better off in the 2nd or 3rd spot, I don't really agree with that, I think X-23 is best left in the 1st position, where she has access to all her assists from the get-go. Even if the DHC glitch were to be removed, I still think she's better off in the 1st spot, as opposed to people saying she should be in the third to anchor the team with X-Factor Lv.3 and Silent Kill. Oh, speaking of Silent Kill, it's probably one of the best Lv.3 hypers in the game. Makes her invisible. it's completely unblockable, and can be combo'd into as well! Another reason why assists are so good for X-23; the right ones can help her combo or lock down people in place for Silent Kill.
Offensively, I would compare X-23 to (S)SF4 Cammy. Cammy doesn't have an overhead and similarly, X-23 doesn't have an immediate overhead. Very early on, people would wonder how Cammy was supposed to open somebody up once she got in. She didn't have an overhead to make people think twice about crouch-blocking all day against her, so people believed crouch-blocking basically killed Cammy and that she was a pretty bad character. Then as Cammy play evolved, people realised that what made Cammy really scary up-close was the fact she could blow up defensive measures like crouching teching using divekicks. Not only that, but Cammy had strings that left her at an advantage and should the player press buttons, she could slam them for counter-hit only combos for big damage. Once the player became cautious of pressing anything, Cammy could mix in throws, which lead to mix-ups and unblockables off knockdowns. There was more to it than that, but that's the short version of it lol.
I think X-23 is similar in that regard. Without assists, X-23 doesn't have an immediate overhead she can use. It can be difficult to open up people. This is where feint cancelling comes in. X-23 can cancel the start up of her Mirage Feints using S. Cancelling a normal, into Mirage Feint~S, acts like a cancel, and shortens the recovery of the normal. Using this, X-23 can turn normals like her standing H into great pokes. She can also use it to generate a great amount of offensive pressure and even use them to produce completely tight blockstrings where if the player gets caught blocking them, they have no choice but to advancing guard/cross-over counter. Doing this leaves her at a big advantage on block, so if the player makes the mistake of trying to press a button after a cancelled normal, they'll get hit for counter hit damage.
If you do an advancing guard without blocking(M+H), you'll notice that H comes out instead. A similar thing happens in SSF4 where if you do a crouch tech(cr.LP+cr.LK), you'll get a cr.LK. It's only when you block a move that advancing guard activates to push the oppoenent way, and it's only when you're thrown that crouch teching activates to escape the throw. Now a big part of why Cammy was so strong against crouch teching was because of her divekick and strings which left her at an advantage. If you mistimed your crouch tech against Cammy, cr.lk would come out instead, which had the risk of the dive kick going over and hitting it for a free combo, or a string catching the cr.lk and getting the opponent hit out of it. Cammy could alter the timing on her strings and offensive pressure and mix in throws to keep you guessing as to when you should try to escape a throw. Standing tech was also risky, as pressing LP+LK to escape throws gave you a grab if unsuccessful, and since Cammy's divekick couldn't be grabbed, it would beat out the throw.
X-23 can also alter the timing of her strings to trick opponents into advancing guard, so that the timing or slight delay causes an unwanted failed advancing guard that she can punish for counter hit damage. X-23 has another way to really mess with her opponent's advancing guard timing and defence in general. X-23 can cancel her normals before they even connect. Though X-23 runs the risk of being jabbed out of it, it's very difficult to react against because of how quick she cancels. The opponent might be expecting a standing H to block, but ends up getting faked out trying to block an attack that never comes, and instead, eats a throw lol. Another example; you do a string of st.M(1 hit)>H>Mirage Feint~S. This string is completely tight. Now, your opponent goes to advancing guard the second hit, which would be the H. But X-23 cancels the H before it connects on block. Let's go back to what happens when you try to advancing guard something without a block. A slow normal comes out. After all, how can you advancing guard something, that isn't there lol?
And like Cammy, X-23 also has divekick specials that leap over normals. So, let's go back to the example, the opponent misses his advancing guard trying to defend against an empty attack, causing (cr.)H to come out. H attacks are slow up close in general. So, the opponent is crouch blocking and a cr.H comes out, X-23 immediately after the cancelled H, goes into Talon Attack L or Talon Dive. Those attacks leap over the crouching normal and you get a free combo. Or you cancel into a normal faster than their H and get a counter hit. And once you condition the opponent to be wary of this, you have more freedom to do more varied stuff offensively.
See, the opponent may not have to switch up their guard, but if you can make them scared about pressing buttons in fear of the consequences, that's effective as well. And that's a part of the effectiveness of Mirage Feints when used offensively. The funny thing is, I remember a player on another forum mentioned a combo that relied on Mirage Feint Cancel~S. He got shouted down for mentioning a weaker combo and those who shouted him down said they wanted to help the character evolve, rather than waste time using inefficient combos. And now Mirage Feint Cancel~S is a big part of the evolution of her offensive game.
There's a lot more to say, but that's it for now.