The latest type of spriting to hit PUK is Expression-Changers. Follow this tutorial to find out how you can make them.
1. Choose a Pokémon to be the base and another with a big gob! Let's choose Quagsire and give him Gengar's toothy grin! Copy and paste from a site such as www.pe2k.com
2. Zoom in with the magnifier tool and cut out Gengar's toothy fizzog. Make sure all the purple that may be around it is erased with the pencil tool.

3. Before you go any further, make sure this is selected:

4. Zoom in again and slap Gengar's choppers on Quagsire's mug. Like this.

5. Finally, zoom in and with the pencil tool, make his eyes look something like this.

The sillier and more comical the better! Save your work and you're done! Simple, eh?