tio que progrms usa s s s s s s??

I would advise cleaning the work by reducing single pixels that are spread all over the place. It seems that your palette got out of control.
The scene and chars look good!

Credit where credit is due, its beautiful and fresh. Really like the rock rendering 

This piece is off to a nice start, but it also has a pretty massive color count (421) that seems like it may have come from blending layers, as well as a number of stray pixels towards the center.  Is there a chance it could have the color count brought down a bit, to be more in keeping with ideal of every color being intentional?  This might even help the characters pop a bit more.

yay, such detailed reply. Thank you, eishiya. Yeah now as it stand it would probably do a mess in the game. This project is on hold, I did this mockup just for my pixeljoint gallery. Anyway I appreciate all these tips, reminded me very important things again. If it would come to the game alone then I would need to tweak all these elements and do revision on all current assets.  

The problem's that both have approximately the same value range. The usual solutions are to reduce the overlap by making the backgrounds sit mostly in one section of the range while the characters sit in another (e.g. dark characters vs light backgrounds or vice versa) and/or to increase the value range in the characters and decrease the value range in the background. Most games use a mixture of both.

It's possible to do this without significantly changing the apparent value range, by only making these changes to those parts of the background that will be frequently overlapped by players, and keeping the non-overlappable areas busy and bright. For example, bushes and tree trunks could be consistently dark (or light) and low-contrast, while tree-tops and other framing elements can have a wider value range.

For example, the forest areas of Momodora: Reverie Under the Moonlight has a fair bit of contrast and detail near the floor, but has mostly solid-ish dark areas immediately above the floor, where the characters will spend most of their time (screenshot). The characters all have prominent light-coloured chunks in their design so that they stand out well from the consistently dark backgrounds near the ground. The backgrounds have a lot of solid areas and are overall fairly low-contrast, compared to the characters. But overall the world doesn't feel dull because the combination of the bright spots in the upper background and the high value range on the floor where contrast with the characters isn't an issue gives the screen a wide range of values. Since your characters seem to employ mostly light colours as well, perhaps a similar solution might work for you.

Edit: Here's one possible solution for darkening the near background. I lightened the two red characters a little to increase their contrast against the background, as well.

yes, that's the hard part.

The characters are a bit hard to make out against the background D: