highly sweet Dragonscale Husk ACF in Dragon Magic.
You mean the worst written ACF in existence? the one that stops you receiving other AC bonuses from any source and doesn't increase if you PRC out of your base class?
I had to go and actually re-read the ACF when I read that post, because I remembered it sucking so hardcore that I just turned the page. Upon a second reading, the terrible writing of the feature actually has some pretty hardcore benefits, too.
For example, even though you can't wear armor with it, it's not an "armor" bonus to AC. It's, in fact, a completely untyped bonus to AC, which means that it applies to touch AC and can be stacked with spells or items that grant armor bonuses to AC without being armor. That's where the second part comes in: it doesn't stack with feats, racial traits, or special abilities, but it can stack with spells and magic items, so a level 1 Fighter under the effects of his Dragonscale Husk and a Mage Armor spell has an AC of 20, with a touch AC of 16.
As for advancement, all classes that grant heavy armor proficiency stack for the AC bonus, and a lot of PrCs do grant proficiencies.
That said, all this puts it into the "abusable" column, as opposed anything particularly godly.
