At crossguard there could be used different color and this is not necessarily bad thing, in a game that would be the difference in two type of weapons with minor differences in strength. Appretiate the feedback!

Seconding jph on this one: you should definitely be paring down the palette here given how small the final image is. You can definitely get creative with that - e.g., the dark brown on the engraved pattern in the handle and the purple outline on the "crossguard" could be the same color.

Really minor change, but you could make the knife look much sharper by adding a single pixel in the top right corner. The harsh 90 degree angle will stand out to the viewer and make it look pointy, which is ideal given it's a frickin' knife.

overall it is a good piece. I would suggest taking a look at the number of colors you are using and what colors they are. when I zoom in on the blade, for example, there are a number of greys that blend into each other so well that I could barely tell them apart! using fewer colors in an area such as that could make the image more straight forward. best of luck, hope to see more pieces from you as your skills improve!