Attached is a dragon I've created. It's based on the planar dragons out of the Draconomicon, so there's some room for variation. I created it off of a concept I had where an evil wererat cleric forced a dragon to contract lycanthropy.
Attached (assuming it did attach) is a Word '07 document with the stats. I'm very interested in how it works and balances for everyone. I don't have challenge ratings associated with it, but for Dungeons and Dragons 3.5, I would use one of the planar dragons as a base for CR and XP.
I suppose by the strictest sense, the lore would have to be changed for OGL purposes, as wererat is a term controlled by WotC, but you could easily just say an evil cleric wanted to crossbreed some creatures and created this freaky mutant.
Yeah, I realized this later when I discussed the creature with The Overlord. I have yet to complete some of the other creatures. I was intending to do a variant based around each of the lycanthropy types. In this example, I gave the creature progressively more powerful dexterity, as that is where the wererat excels.
I've used this particular creature a few times in the game, and so far it seems fairly well-balanced. I think it would be an excellent way to keep wererats in a little higher level campaign. Granted, wererats advance based on levels, but this gives them an unexpected power-house.