So I scrubbed the threads and most are people debating about stacks vs. replacement (it replaces). The question I’m having is when combined with greater mutagen do the natural armor bonus stack (Sturdy rage+4 with GM +4 for a total of +8 as both are listed as a untyped bonus)
So then for my math to be policed a greater rage mutagen (going with STR 6/DEX 4) would be:
STR 8
DEX 4
CON 2
INT -2
WIS -2
NA 8
-4 to will and intelligence score with damage; -1 Dexterity
That looks correct to me.
The extra Natural Armour from Sturdy Rage replaces Swift Poisoning, so it looks like it's +4 on top of what a Mutagen normally gives you. If it didn't stack then it'd be a waste of a class feature.