Quote Originally Posted by willpell View Post
One thing that remains unclear about dragons - do the save DCs of damaging breath weapons follow a consistent pattern? A formula of "10 + half HD + CONMOD" is listed but seems to only apply to metallic dragons' nondamaging breath; for damaging breath it says "see the dragon variety's description", which isn't terribly helpful for figuring out exactly when the increase occurs for a dragon that's leveling up. (Perhaps it clarifies in Draconomicon somewhere; I haven't actually read the book, just referenced one section that seemed relevant, so I might have missed another one that actually was.)
I haven't calculated it for all of them, but it looks like the Chromatics obey 10+half HD+Con mod as well. If you find a counterexample let me know.

Cieyrin has answered the Dire Rat question ably. In general, Animals and Humanoids can have nonstandard save progressions.