[Kirble]

I'd suggest using the mouse for Graal graphics more-so aimed towards sprites. Doing anything like a scene or a larger character for example on a 400x500 canvas I would use the tablet (pen) to do the outlines, use the mouse to tidy up the lines to 1 pixel or whatever then depending on the effect you are going for (Painted or pixelled) use the mouse or the pen accordingly.

Mouse for dithering etc (Pixel looking graphics)
Pen for more painted looking graphics. =]