I needed to make a Pikachu doll for this very reason. I couldn't find stuffed animals that were high quality. What I did find were some great paper craft models and patterns. I constructed the paper model and used it as a prototype for my fabric Pikachu, modifying the pattern to make it work with stretchy fabric that had to be stuffed and sewn together.
This project took about a week and I'm very happy with the result.
The tail was a particularly big challenge. Pikachu's tail is rigid in the game and cartoon and fabric is anything but rigid. What I ended up doing was creating a wire frame and sandwiching it between a ton of fabric interfacing so that the tail would still be somewhat soft.
**Here is a great tutorial on the paper-craft pattern I used to create this doll. If you're interested in making this pikachu, this is a great place to start: http://papercraftprintable.com/pikachu-papercraft-model-instruction-and-tutorial/ **
Mudkip is next.