Kybyrian
The first flaw is the lighting, in that where you have placed the source, it does not match up with the stock you have chosen. One of the important things when making a signature, is that it is coherent. Looking at your render, the light source was clearly intended to be placed above, and to the right of Skull Kid, but instead you have placed it centered, and to the left. The other problem with this lighting, is how bright it is. My eye is instantly drawn to it, making it the focal point for this banner, which should not be the case.
Also distracting is the text, which causes my eye to move from your light source to it, rather than your stock. When adding text, it should not simply be placed in, but instead must physically and mentally add to the piece. The reason I placed my text the way it is, is because not only did it to the flow, but the large area of black it is covering was distracting from the focal.
As I just mentioned, flow is also important. One way or another, the other aspects of the sig should not only add to, but lead to your focal. This is very important when making sigantures, and is something many sig makers often neglect. Flow need not be always noticeable, like it is in my signature, but the construction should in some way, come back to your focal point.
Finally, while it is crucial that you make your stock stand out from the background, and other parts of your signature, it must also blend, for even the background still adds to your focal. Everything in the sig should be in unison, and so the contrast between stock, or background, or text should not be instantly apparent. Whether it is through effects, brushing, or smudging, the transition from background to focal must be a smooth one.
Josie
The first thing I will go into for you is the stocks. While it is certainly possible to make a good signature with multiple stocks, placing them on opposite ends will prevent this. Your eyes get confused as to where to go, and thus you basically have no focal. The quality of the stock is also important, because even though your Deku Link appears to be just fine, your Skull Kid is pretty low in quality. I did notice, however, the Deku Link gets cut off on the end, which brings me to my next point.
Pop-out signatures are a wide spread technique, and in some cases, can work out really well. One of the problems you have is that you have essentially pasted the renders on there, without giving much thought as to how they will blend with the background, and so you have stacked images. I’ll use Xinn’s as an example, because she has a pretty good example of it works. While she uses this pop-out technique, she still keeps it within the confines of her canvas, so it is still a part of the signature.
Color is an important element as well. One of the things I did like about Kybyrian’s signature was that the green he chose really complemented his render, and helped blend it slightly. What you have chosen is a really bright magenta, and a light blue for your text, which not only contrast each other, but do not compliment your stocks at all. The white brushing in the background also adds nothing to the signature either, except filling up empty background space. While this isn’t necessarily a bad thing, if it isn’t doing anything for the signature, there’s really no need for it.
As I also told Kybyrian, text should add to the work. Your text is acting like a focal in this case, because you have it placed in the middle of two stocks, have used a really contrasting color, and it takes up a lot of space. For whatever reason, and I have no idea why, your text looks really blurry and low quality.
Zelda’s Child
I compliment you for using a bit of flow in there, but the problem you have is it’s not really going in the right direction. In the render you’ve chosen, Kafei is leaning in. His direction is going the opposite direction of what you have used. The thing about flow is much like lighting, in that it must cooperate with the stock.
It’s always good to use effects, but the purpose that they serve, is they are adding into the flow, and are also not distracting. In your case these brushes are bright, in fact the brightest aspects of your sig, and so they really grab most of the attention. In addition, they are randomly scattered throughout, instead of contributing to the flow.
Your render is kind of low quality, but is also placed in, without any blending. Furthermore, it’s a pretty emotional scene, so I think giving your signature such a mood would really bring it to life. Other than that, your text blends pretty well, but it doesn’t really add anything, and is just sort of there.
Xinnamin
This one kind of hurts me because I imagine quite a bit of work was put into the artwork you made, and I think it’s a really good stock. The problem is my decision is based on the signature itself. I think it’s great that you incorporate your art into your work, but I think if you do so, it should be present within the entire piece.
The background you’ve chosen is just a pasted screenshot, with a green color that does not compliment very well. Furthermore, I think you had a really good opportunity to add flow with your stock, because of the tails, which could really help with this. You have also used far too much text, which takes up the majority of the space, and really adds nothing whatsoever. It seems like you simply used the text to make up for the lack of anything else.
TheGreen
The issue here is the same as Josie’s, because you have used multiple renders, you thus have no centerpiece. You’ve made the child standout amongst the others through opacity and size (it is good to emphasize), but my eye is still drawn away from it because of the other stocks used. The problem you have, much like with the other signatures, is that you have merely pasted the render in, without allowing it to blend, and simply have pasted image on pasted image.
Also the same is that your text distracts and does not help the signature in any way. Overall, I can’t comment on anything else because you haven’t really done anything but placed in renders and text on a plain background. I will say, though, I liked your use of size to add flow leading to the stock.
All of them are epic but my vote goes for Steves banner.
The sig looked empty, so I added the sparkles. Now I see that they're too overpowering. 
