Hmm, not particularly original as a concept, but that's alright. If you want to go with that, try to put in a twist. For instance;
- His creations live for several hours then drop dead. The Doomguard want to recruit him, as do the Signers. Even more fun; those that don't die of natural causes meet strange and unfortunate accidents. The character is torn between the desire to create and the guilt of watching bambis get trampled by herds bariaur suddenly appearing through a portal.
-The 'animals', though seemingly alive, remain two dimensional and cannot leave the surface they are painted on. However, he has also seen someone who was leaning up against a wall get mauled by a 2-D panther mural from around the corner.
- He can only paint creatures from his home plane. That's why he came to Sigil, to expand his abilities and be able to paint other creatures and races realisticly enough to breathe life into them.
- He can only paint an individual from a live model, which then becomes a perfect clone of the original creature, including memories and personality. Alternate twist: the clone becomes an 'evil twin', or a 'good twin' should he do a portait of a fiend or other evil creature. This could make him some fiendish enemies, and some fiendish-looking friends at the same time.
Feel free to pick one (or more) of mine or come up with one of your own!
Hm, the only idea I've been able to come up with so far is a character that specializes in drawing living things which he can then bring to life.