The black lines around yoshi are too bold. Text is fine, however Yoshi is too big, and the BG is okay. A bit long though - even if to suit the text.
i actually like the big black line on yoshi's outline, just make the words also have a big black line around them too!
That doesn't help it blend with the BG though - which is what this sig mostly lacks. Sure the render and BG are GREEN (sorry), but the black lines are pretty much cutting it off from that.
how is it 'long'? the maximum sig dimensions are 500x200, and oh, what could i do with the backround?
Find a new background or make a new background, hey i think you should know about deviantART: where ART meets application!, there in the search box type in Signature Tutorials, and the like one million tutorials will come up, most are for Gimp, Trust me, if it help me, it will help you!
I think that the background is fine, but the outline on Yoshi is about 3 pixels too big... I think that the size is perfect too. You might consider making the border a bit more noticeable though, and maybe only having it on the top and bottom instead of all 4 sides.