Except for PC Free Spirits. Their dual nature does not disadvantage them as much (if at all) as postulated in this thread.

They're not that kind of dual-natured (not at all, if we used the words properly, heh). They're astral-natured who can materialize (or another power, depending). They're the same (backwards) as mages who can perceive; physical-natured who can temporarily add astral. It's the *real* dual-natured ones we're talking about. Maybe an inhabitation free spirit would count, but what we're actually discussing is ghouls, hellhounds, that kind of thing.

The trouble with hellhounds is that being dual-natured is a big part of their schtick (being able to detect astral threats). On the other hand, their Fear power means they aren't totally defenseless.

The biggest problem is PC ghouls, drakes, and shapeshifters, at least the ones who can't sling spells. I think it's okay for them to have a glaring weakness to balance the other cool abilities they get, but others might disagree. But if you do need to "fix" it, changing dual nature is better than making astral attacks ranged or otherwise overpowered. I think things like suppressing it with the equivalent of a sustaining penalty, and suffering withdrawal if they do it too long (like technomancers who turn off their VR immersion), is a decent compromise.

Along the lines of a Dual-Natured sapient suppressing itself from the astral, I hadn't thought of imposing the sustained spell kind of penalty but something that might be a bit bigger.

The short and simple of it being that a Dual-Natured being that suppresses its Dual-Natured ability also suppresses its magic related abilities (though it's not as big a deal to a TM, there's no sustaining penalty and their complex forms are pretty much useless when they suppress their wireless if they don't have the Skinlink echo and can touch an electronic device), losing anything that deals with foci, spirits, and spellcasting and such. And of course that they'll become rather fidgety, agitated, and irritable if they hold this for too long (much like a TM). No rebinding foci or spirits, mind you, they're just deactivated and inaccessible while their Dual-Nature is suppressed.

Might work for some, and it might not for others. Just an idea.

Well, the most simple solution is to just cut it out.
If not even spells are considered dual natured (we had this discussion on the question if you are able to counterspell from astral) then there is no room for anything beeing dual natured. (Beside maybe Cybercombies or spirits)

And even insect spirits (flesh form) are close to unuseble if they are unable to blend in.

If we're going to do that, then lets turn "dual natured" into "astral perception" but revoke the ability to cast spells at merely "astrally perceptive" entities. Instead, what mages have (currently called Astral Perception) into some more fully astral presence which can be targeted astrally.

Similar to (gasp) Kotoa from That Other Game which have a racial "See Ethereal." They can't do anything to the ethereal plane, nor be effected by it, unless the kotoa is a wizard and gets the Trans-dimensional Spell feat (just like any other wizard) and prepares spells with it.

What this does is allow some animals to be capable of seeing the astral plane and being able to react to it, without being a danger to it, or from it. You want your hell hounds to be able to defend the astral plane too? Well, train them to be able to assert their will on it, etc. etc. which gives them Astral Action or something (and astral combat).

With a lot of those creatures, you really wonder why they're Dual-Natured. Why are hellhounds dual?

Ghouls are the only really problematic one; hellhounds have Fear. Ghouls have Dual-Natured only as a compensation for blindness; they'd be far better off with Echolocation instead.