So... not sure how I missed this while reading the Book Of The Dead rulebook, but I recently saw the "Old Friend" familiar option and (besides having a mini emotional breakdown after reading it) had a few questions I wanted to ask...
As someone who had built an 'Old Friend' in Pathfinder 1st Edition using Figment Familiar, this made me want to build a character focused around this idea. However... I'm not quiet sure how familiars function or what makes them work in 2e, so I wanted to ask a few things:
1) What does it mean "Required Number of Abilities" for specific familiars? From what I'm reading, it sounds like it costs a number of Familiar Abilities? So I'd be down 4 Familiar Options in order to take the Old Friend Specific Familiar? (It has 4 listed next to it).
2) What can incorporeal creatures do to benefit the party? I understand it'll pretty much be a non-combat pet thing outside a few spell casting gimmicks, but I'd hate to invest an extreme amount of resources (~3 Class Feats and <assuming above> 4 Familiar Abilities) for something that is just the equivalence of flavor.
3) What other benefits would Familiars have to the party if I were to choose a Familiar focused character?
Yeah, familiars got their utility reduced quite a bit in PF2.
Regarding question #3, the best options are ones that benefit the primary character. Familiar Focus, Restorative Familiar, Cantrip Connection, or other things like that. Similarly, Skilled will let them use skills that your party is lacking - though it will be at a lower bonus than what any actual character will be at. There are also the skill assistance options like Accompanist, Ambassador, and Second Opinion that can help your primary character be better at skills that they are already good at.
For doing things themselves, there are things like Spellcasting, or Spell Delivery. And the sense improvement abilities that can help for scouting or at least enemy detection, such as Tremorsense, Darkvision, and Scent.
The anchored incorporeal trait doesn't let the creature move through walls, but the main advantage I see is the familiar can cast invisibility on itself once an hour. I believe it is the "cheapest" familiar to get that option. Combined with flier and I think the main use will be scouting, though it has a limited range. To utilize that you'll need a way for it to understand your commands and relay information back, which probably means speech and/or share senses are necessary. As such you'll get the most mileage using something like familiar thesis or the familiar master archetype that gives you additional abilities to play with.
Note familiar scouting is a contentious issue on here because how minions behave in exploration mode is poorly defined by the rules. If your table allows it, then it is an extremely powerful ability. Intelligence is extremely useful, especially for prepared casters. If your table doesn't allow it, then your better off with master boosting abilities like breith describes and the old friend becomes pointless.
Check out the Familiar Master Archetype. Familiar Conduit is a metamagic ability that allows you to use your familiar's position as the origin of your spells and Mutable Familiar allows you to swap some familiar abilities on the fly.
Honestly, might still consider making a Familiar with a ghost pet, if nothing else but to experience having Kira in my games again. I used to have a character with a pet which was a tribute to my old cat, and when it died in the story I was in (unlucky combat with a Mauler Familiar), I opted to make it a Figmented Sage familiar to represent it being a ghost.
So it would be interesting to have a Ghost familiar, even if we don't have Maulers in PF2e.