How to advance a templated monster by HD, given the type change?

[ksbsnowowl]

I'm looking at making a Half-Fey Quasit as a type of cruel and capricious fey that paralyze people with their Dex poison, and steal all their valuables.

Quasits are 3 HD Tiny Outsiders that advance by HD, up to 6 HD.

Half-Fey changes their type to Fey, and changes their HD from d8's to d6's.  It does NOT change the outsider Good BAB and all Good Saves to the fey Bad BAB and Bad Fort save.

So, a 3 HD Half-Fey Quasit advances in HD...  Does it advance in "Outsider HD," getting all good saves and Full BAB, or does it advance in Fey HD, and start getting Poor BAB and a Poor Fort save?

Similarly, the rules on advancing a creature by HD... Outsiders gain +1 CR for every two HD added, but Fey gain +1 CR for every four HD added.  Which do you use?*

*I suspect it will be tied to how you advance them, with Fey HD or "Outsider" HD.

I'm guessing the proper way would be to just take the base Outsider Quasit, advance it to 6 HD (adding +1 CR), then applying the Half-Fey template to that.

Thoughts?

[Ithamar]

It sounds like you do not employ the Type pyramid from Savage Species.  If you did, I think that would help with your question somewhat.

But in general, adding a template should not make the enemy weaker or worse off than it would otherwise be.  So I think your last statement is the way to go:  Advance the quasit as an outsider and then add the template.  Makes the most sense in my mind.

[ksbsnowowl]

Well, there are other templates from the same book that specifically seem to trump the type pyramid.  The example Half-Troll is a Half-Troll Bearded Devil, whose type became Giant.

[nijineko]

the template adjusts the base creature, unless the template specifies an adjustment, the advancement defaults to the base creature.