I haven't been here for a while. I guess I better do some rating ^^
Renneh: For some reason, I like this quite a bit. It's probably because of the spatter clipping masks, or the multi-coloured soft brushing. Or maybe it's the smudging in the background. I don't know. But it all fits together quite nicely. Multi-coloured-ness for the win. The biggest thing to work on is probably filling up the empty space. Text might work well, but I just have something against putting text into banners unless it's completely necessary. Or, if it's a typography piece o.o;; I don't really know what else to suggest. More clipping masks? Ah, and Shana (that is her name, right?) looks a bit pale. Work a little bit more on blending the render in. Otherwise, it looks great.
Poke'd: Happy (belated?) birthday ;P
Sprite-ish banner - I personally don't like sprites in banners. Unless it's Guilty Gear or King of Fighters sprites. Or some other fighting game where the sprites don't look... weird. It's also a bit muddled up, since there's four focals, or something. Just use one or two x___o It's also looking quite dark. Brighten it up a bit ^^ The effects look interesting, and helps add flow to the purple-ish sprite (the Ditto-Smeargle fusion). But I guess it just doesn't really look right. There's also some empty space, so maybe shrink the canvas down a bit, so it doesn't look quite as empty.
Hitsugaya banner: Aah, Shiro-chan >3< The smudging's quite good. But work on colours. As Renneh said, don't make it look monotone. Add some green or deeper blues instead of the smudgy gray-blue-green colour there. The flow is pretty good as well. It's mainly just colours. Oh, and filling up the emptiness. Try putting clipping masks or smudged C4Ds there. Or something similar.
Gummy: Monotone o.o As 'angry' the colour red is, it needs some other colours to go along with it. Yellow, or orange? I like the spatter-like brushing in the background. That one looks great, like blood dripping from the walls. The blending behind Carnage looks alright, but it needs blending under his jaw, and around his arm, since I can see a yellow-ish outline around the render. Work on the depth a bit as well, it's looking a bit flat at the moment. Try using a large soft brush on black, and brush around the edges. Reduce the opacity if needed. The burn tool is pretty useful as well, as long as you don't spam it to death. And don't sharpen it too much. It's looking a bit pixelated in some areas.
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Just messing with this style~