It's cool you're working on a Big the cat WAD, but I suggest you make him 'bigger'. :P He's suppose to be nearly twice as tall as Sonic and plenty wider, which also allows more room for detail. Here's a pic of him if you need something for reference.
http://upload.wikimedia.org/wikipedia/en/c/c1/Big_the_Cat.png
I too can testify to MSPaint's awesomeness, I'm working on my Blaze WAD and some other things with it right now. I've been using it since Windows 95 was the latest thing, lol. The interface has quick access to every tool and it's easy to use. I wish more programs were like it and that somebody would write a Linux equivalent of it. MT Paint is kinda confusing, to me anyway.