I've been looking at doing a druid mounted fury barbarian list, and the mount I've chosen come up in herolab says it cannot be selected because it is not in the cavaliers mount list.
But I can't find anywhere that says the barbarian mount list is the same as the cavaliers, so I'm asking the question.
Bestial Mount (Ex)
At 5th level, the mounted fury gains the service of a feral mount. This ability functions as a druid’s animal companion, using the barbarian’s level –4 as her effective druid level. This companion must be one that she is capable of riding and is suitable as a mount. A Medium barbarian can select a camel or a horse. A Small barbarian can select a pony or a wolf, but can also select a boar or a dog if she is at least 8th level. Whenever a barbarian is raging while mounted on her bestial mount, the mount gains a +2 morale bonus to its Strength.
Unfortunately it looks like you are severely restricted on mount choices for Mounted Fury, unless you read the second and third sentences as somehow being additional options, but that doesn't really make any sense as those are all standard druid choices.
One level of what? I don't understand your question?
If the question is what if you took one level in a class without restricted access to animal companions...
I think in PFS you are restricted to one animal companion, and that you have to add your effective druid levels together, and I think in this case you would be constrained by the limitation from mounted fury (but I'm not positive on that).
Outside of PFS...well I'm not sure there is an official answer.
The way I would run it is that you mounted fury levels can only add to effective druid levels on the approved mounts. If you took levels in a separate class that granted an animal companion you could either choose the same animal companion and have those levels stack, or if you chose a different animal companion you would have two with the mounted fury levels counting towards the horse/camel/boar/riding dog and the druid levels counting towards the other.
No it wouldn't. You can more than easily extrapolate the rules to other classes - it's not rocket science. They really don't and shouldn't need to hold our hands while we go potty and wipe our tushies for us after.
Sorry, bugbear of mine. Some things should only apply to the specific question raised in the FAQ, this really isn't one of them.