using a mouse isn't an excuse
all my computer stuff i have done to date is with a mouse... some even in ms paint... i don't see why that would make your art any more worse... it just takes a bit more time and effort... theirs a lot of stuff wrong with this... I'm going to ignore the quality... right... the bunny seems to only have one front leg or two on the same side... the sky gradient it too harsh too quickly... adding more colors would have helped and also in some softer colors... the plant seems very odd in the blank landscape that seems very bumpy... might have smoothed some of the lines a bit more with the pen tool just to go back over bits to repair them... also might want to make the feet a bit larger as most seem to be flat...
if you really want to work on pixel art... make sure you got a good color pallet.. reading some of these comments below have great ideas to help improve... once you got your colors ready make sure you work in fine detail... don't bulk colors unless your going for a smooth clean design.. but as this stands its getting a tiny 2 for been part of the the flood... better luck next time