So what do you feel like are the essential rules to run a Golarion game?

[Eltacolibre]

I mean beside the obvious like the core books(APG, ARG, Ultimate Magic, Ultimate combat etc...)

Do you use the faction rules/prestige? Honor? Downtime? Sanity from horror adventures? Anything else noteworthy?

[justaworm]

CRB + GM is right + saves rules debates for post-game

[deuxhero]

Core Rulebook and some setting specific rules like "Clerics of a concept don't exist" are all you need.

[Ascalaphus]

Are you talking a "Pathfinder" or a "Pathfinder on Golarion" game?

For the latter, I'd say the Inner Sea World Guide is essential. It's a very comprehensive setting guide, covering many different aspects of the setting (social, geography, deities, economy, politics, races, languages, factions).

From there on out, you can specialize as you see fit. Don't add every possible rule system you see; pick up those that emphasize the campaign you want to run. If you're not interested in a political game, why use faction rules? That's just extra bookkeeping. If you're not playing in Numeria, the technology rules mean nothing to you.

Rule system and campaign style influence each other heavily. By default, I think Pathfinder is a bit of a "Die Hard" style game - someone gets hits, they grunt and clearly it hurts. But by the next scene it's just a scratch on their face that doesn't hinder them all that much. Pathfinder is a bit of a power fantasy game. If you add horror rules and all kinds of lasting injuries that are hard to quickly remove with magic, you get a very different sort of game.

If you've become interested in a particular AP or region, I'd recommend picking up the appropriate book (i.e. the Numeria book if you're running Iron Gods, the Korvosa book if doing Crimson Throne etc.); Paizo is very good at setting books, they give the GM lots of new ideas and bits you can sprinkle in to give more dimension to the country.

The recent threesome of new-style-adventure books (Occult, Intrigue, Horror) have a lot of interesting subsystems. Intrigue clarifies a bunch of older rule points about illusion and stealth and has a bunch of interesting minigames if you want to make social clashes more than an opposed diplomacy roll. The Heist chapter is particularly good. Intrigue also has Research, which combines well with the Occult Adventures section on Rituals, if you want to make magic more mysterious than simple well-understood spells.

[Eltacolibre]

Thanks everybody for the input.

Yeah must admit that the combo of Occult, Intrigue and Horror sounds very appealing to me just going to work out, the best place to play this kind of campaign on Golarion.