Ok, I guess an Improved familiar gets those bonus Natural Armor and the Special Abilities that are depending on the master's CL.
But what about the Int score?
For example Int score for a familiar of a 7th level wizard is 9, which is alot for an animal, but in the Improved Familiar list there are quite a few with higher int scores by default. The highest being the Brownie and Lyrakie with 14 Int.
So... does an Improved Familiar keep its Int score if it's higher, or does it actually get dumber?
I have wondered this myself, anybody know?
I was ruling it as going by the normal familiar Int advancement (i.e. dumber) but that seems weird.
I've always assumed you would use whichever score was higher. That's the way it works with all the other familiar stuff (saves, skill ranks, etc)