Where can I learn to draw weird little creatures?

A lot of practice. And, a scanner or drawing tablet :)

The first thing to do is to draw lines like he does. His vary in thickness, thinning towards the edges. Yours, at least in your link, are sketchier and more uniform. This is a small but very significant difference. If you draw on the computer, a pressure sensitive pen and a the proper drawing software will make this part easy. The second element is the watercolor was for the shadows. Again, a computer program like Painter makes this trivial. Paint faintly behind your outline, with low opacity. Paint again to darken. Use a smaller brush than you think is necessary. Then just be creative, develop the character of what you're doing, and practice practice practice.

I've been trying to work out my own cartooning style for years. Like you, I was never really interested in developing a realistic or detailed style, but more and more I'm thinking I should have started with the basics: perspective, anatomy, composition. Cartoons may be simple, but cartooning isn't. Looking at the sample you provide, I can see that you're still thinking in two dimensions. The arms of your creature are both drawn perpendicular to the field of vision: they're neither going towards nor away from the viewer. This is easier to draw, but if you want to have Bell's virtuosity, you need to see into the page. Bell converts a lot of his drawings into awesome sculptures, they're not just flat things. Some practice in drawing actual objects from the real world might help you a lot with this. Another thing that might help is to do the little kid thing and flat out copy art you like. I don't mean to present as your own, or even to present at all. Just as a personal drawing exercise, trying to make a freehand copy of some of your favorite cartoonists' drawings can tell you a lot about where you need to improve. Using a pen, brush, or stylus that gives you a varied line width can be very enlightening once you get the hang of it, but never get caught up in worrying about tools rather than working on the art. Andy Bell can draw better stuff with a broken-off pencil tip than I can with the finest sable brush or the biggest, newest Cintiq. And yes, practice, practice, practice. You might get really good without worrying about anatomy or perspective, but you'll never get anywhere without putting drawing implement to drawing surface and making all your mistakes until you learn better.