My friends and I have been playing DnD 5e for a few years now, but now I’ve decided to start GMing PathFinder 2e. We’ve played through most of the Beginner Box, and now I want to continue with my own homebrew content. As part of my world, I want to introduce a fighter “subclass” (probably the wrong terminology for PathFinder). What I want is a tribe of warriors who fight without armor (starting at level 2 or 3), and to compensate for the lower AC they get magical tattoos which increase their AC. It will also be possible (when you advance in levels) to choose to add other tattoos with other magical effects.
So my question is: Is this what archetypes are for? Because I don’t think “subclasses” are a thing in PathFinder? Or how would I go about this?
Archetypes are an interesting beast. They are the primary pathway in the game to taking on feats and features from other classes, via Multiclass Archetypes, but they're a lot more than that, too.
One of the things they're leveraged for is class variants. There's not a wealth of examples in this category, but it's kind of tantalizing. This is where you find PF2's equivalent of the Wild Mage, the Wellspring Mage. It's also where you can straight up just choose 5e style hybrid casting, with Flexible Spellcasting.
But the real core of Archetypes seems to be turning background flavour into defined game mechanics. Here, OP could make a melee archetype that could apply to the Fighter, Barbarian, and Monk classes, providing depth of fighting style and role to this society without needing to develop independent subclasses for each of them.