also, we have a built in zoom feature here at PJ (the -/+ buttons beneath the piece). so we usually require that work be submitted at 1x. also also, be careful to avoid 'bulk submissions' (submitting a lot of stuff at once), as it floods the queue.
as far as pixel tech is concerned, there's a lot of jaggies here. There's AA in a few spots, but it isn't applied consistently. There's also a lot of banding. the composition is pretty cluttered. It's a bit odd that bowser's face is obscured, and the lower half of donkey kong seems unresolved. mario's hand is a bit of a mess, and several characters have wonky eyes.
in case things like banding/aa/jaggies are unfamiliar to you, check out the PJ tutorial
I like the concept, and theme-wise it is pretty well portayed. However, I do feel that for visual purposes, the background is entirely unnecesarry. Its just a bunch of 2x2 pixel blocks of random color. I think a solid, subtle toned or dark background, or entire lack of, would do this picture justice. Here are some other things you might want to look into:
-Some of the shades in the color key dont contrast enough with their partners. For example, the mid-gray tone (is that AA?) could be lightened up a little to smooth it out and become a visible difference
-Like cure said, the built in zoom feature allows you to upload artwork at a 1x1 ratio. Im assuming that its in such a large scale because the site you uploaded it to doesnt have a zoom feature. I personally see no need to zoom at all, the image is pretty clear at 1x1
-again, cure mentioned AA. Depending on style, AA may not even be necesarry at all. ever. HOWEVER, for this particular piece of pixel, I would recommend using AA just to smooth out the image. I also suggest simply smoothing out some of the linework itself, such as Marios hands, DK's face, etc..
-It looks like marios lower body aswell as Dk's and Bowser's are blurred. From what i understand, any type of editting FX besides your generic pencil/shape tool is not allowed. I know that the blur cannot be undone now, but you could go over it with some simple pixel by pixel smoothing using 3 or 4 shades to give it a manual blur/fade effect
-If possible in anyway, it would be nice to see everybody moved apart just a little but (not alot, just a little) because it feels a little to cluttered. That could just be the background getting to me though.
Im sure i missed stuff since im no pro, but I think if you take my advice into account you might see some improvement.
I like this pixel BTW, its a nice break from the generic "mario and luigi being mario and luigi" thing