Invoker Player's Notes

The selling points of the invoker are the spirit companion and spirit invocations. The unique point of the companion is that it is a pet, but where those are almost always a melee fighter, the invoker’s companion is the supporting caster and ranged damage dealer to the martial character.
The spirits invocations allow the invoker to specialize on specific tactics per day, thus giving a more varied playstyle than most martial characters. The spirit abilities, that are powered up via invocations, give additional options in a fight.

The ability scores you need most are the usual martial’s strength and constitution, with charisma being responsible for the uses and DC’s of spirit powers.
The best races for the invoker are those with a bonus to either str or con and charisma. Those with a connection to nature or fey are particularly good options from a backstory perspective, but of course anyone can attract the attention of the fey.
The genie descendant Suli or the plant-like Ghorans have excellent stats and fluff for invokers. Grendels from Dreamscarred Press are also an interesting option.

For multiclassing and gestalt, look for classes that support the invoker’s versatility and front-line role. A few levels of brawler can provide versatile access to combat feats for example. 

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Spirit Bound armor
Price: +1 bonus
A suit of Spirit Bound armor is inscribed with imagery related to the wearer’s spirit companion’s domain, and eases the merger of the wearer and his companion. The wearer can stay in the avatar form for an additional 2 minutes per day, and 3 times per day can cast one of the spirit companion’s spells as a free action.

The battles of the Warring States period took place on many battlefields, and the remains of clockwork ronin can be found in even the deepest wilderness. The spirits of these wild paces sometimes mingle with the remains of the ancestor spirits trapped in the spirit gears, brining the fallen soldiers to life once again.

Spirit Blast
You have learned to channel the destructive power of you companion.
Prerequisites: Invoker level 3, Spirit companion class feature.
Advantages: You can use your companion’s spirit blast.

Elementist

NPC class version of the Elementer (Path of the Wilds)

Focusing on both spellcasting and elementally powered combat is beyond the ability of most. These lesser Elementists instead focus entirely on the martial side of the Elementer.

Hit Die: d8

Skills: Acrobatics (Dex), Climb (Str), Craft (Int), Fly (Dex), Knowledge (geography) (Int), Knowledge (nature) (Int), Perception (Wis), Profession (Wis), Survival (Wis) and Swim (Str).

Skill Ranks per Level: 2 + Int modifier

Level	BAB	Fort	Ref	Will	Special
1	+0	+0	+2	+0	Aegis
2	+1	+0	+3	+0	Spell Twist 1/day 1st level
3	+2	+1	+3	+1	Affinity (Lesser)
4	+3	+1	+4	+1
5	+3	+1	+4	+1
6	+4	+2	+5	+2
7	+5	+2	+5	+2	Spell Twist 2/day 2st level
8	+6/+1	+2	+6	+2	Affinity (Moderate)
9	+6/+1	+3	+6	+3
10	+7/+2	+3	+7	+3
11	+8/+3	+3	+7	+3
12	+9/+4	+4	+8	+4	Spell Twist 3/day 3st level
13	+9/+4	+4	+8	+4	Affinity (Greater)
14	+10/+5	+4	+9	+4
15	+11/+6/+1	+5	+9	+5
16	+12/+7/+2	+5	+10	+5
17	+12/+7/+2	+5	+10	+5	Spell Twist 4/day 4st level
18	+13/+8/+3	+6	+11	+6	Affinity (Master)
19	+14/+9/+4	+6	+11	+6
20	+15/+10/+5	+6	+12	+6	Spell Twist 5th level

Aegis (Su): All elementists learn a potent technique to envelop themselves in elemental force, shaping it into a raiment of energy. This is known as creating an aegis, and while powerful it is not without its limitations.
The the elementist can enter into their aegis form as a swift action. The elementist can use their Aegis for a number of rounds per day equal to their elementer level / 2 + their int modifier, minimum 1 round per day.
While in her aegis form, she gains a +1 bonus on attack rolls and to her AC. This bonus increases by +1 at 5th level and every four elementist levels thereafter to a maximum of +5 at 17th level. While in their aegis form, the elementist is unable to cast spells, use spell trigger or spell completion magic items.
The elementer can voluntarily exit aegis form as a free action at any time. Once she leaves aegis form (whether due to running out of rounds or exiting voluntarily), they cannot re-enter until the end of her next turn.

Spell Twist (Sp): Beginning from level 2 the elementist can learn a Spell Twist in place of a feat. The elementist can use their spell twists once per day at level 2, with one more use per day every 5 levels after. The Spell Twist is treated as if a 1st level spell was used to cast it, increasing by +1 at levels 7, 12, 17 and 20.

Affinity (Su): At 3st level, the elementist learns how to harness the elements to improve their aegis form. Each day when they prepare their spells they selects a single lesser affinity power from those listed and the end of the class description. They gains the benefits of that affinity power while they are in their aegis form. The choice remains until they prepares spells again, at which point they can choose a different affinity power.
Upon reaching 8th, 13th, and 18th levels, the elementist may also select a moderate, greater, and master affinity power, respectively. The elementist automatically gains the benefits of their affinities when they enter their Aegis form.
Affinity powers are categorized into one of four elements: air, earth, fire, or water. If they’re currently benefiting from more than one power of the same element, they gain additional effects depending on the number they’re currently benefiting from as listed in that power’s “synergy” entry.

Archivist Multiclassing and Gestalt

The central problem of multiclassing the Archivist is that they are a full caster class, and there is little that is more valuable in Pathfinder 1e than that. Dipping Archivist might be more useful because of a particular quirk or Rune Casting: The lack of Somatic components. If you want to add some magical abilities to a martial character dipping into Archivist can get you that with less complications than Arcane Magic.

Gestalting comes with the same considerations as other full casters: It requires a lot of actions and as such works best with more passive classes. The ability to cast in heavy armor and with both hands full again opens some options that don’t work well with other full casters.
An interesting option is the Runesmith from Interjection Games, a class that uses runes to enhance theirs and other’s equipment.
Pet classes like the Summoner or Vanguard can be flavored to have their pet summoned or created with rune magic.

The broken scribes are a loose group of Scribes who use Aboleth glyphs to draw and shape Ether, a strange power from beyond reality.

Runic Spell (Metamagic)
You can cast spells in runic form.
Requirements: Ability to cast 2nd level Scripts
Advantages: A runic spell is cast with no somatic components, but with a vocal component. Once successfully cast it gives the caster a Runic Charge of an appropriate Design.
Level Increase: +1

Therkla Proudfoot often surprises her opponents with her runic enhanced strength.

Archivist Class Features

As a full caster the Archivist has relatively few class features. The Archivist has d6 HP, 2+int Skill Points and ½ BAB. His Class Skills are Appraise (Int), Craft (Int), Fly (Dex), Knowledge (arcana) (Int), Knowledge (history) (Int), Knowledge (nature) (Int), Knowledge (planes) (Int), Linguistics (Int), Perception (Wis), Profession (Wis), Sense Motive (Wis), Spellcraft (Int), and Use Magic Device (Cha).

At first level the Archivist gains his Rune Magic, his first bonus feat chosen from a Rune Casting focused list and has to choose a specialization called a Study.
A Study is the specialization class feature of the Archivist, giving the them additional abilities at specific levels, as well as an additional bonus when overloading a Script with the right type of Runic Charge. Besides the six Studies for each of the six Designs there are 12 more specialized Study options available in the 3rd chapter.

Altered Script is gained at fourth level, allowing the Archivist to change the Design of their Runic Charges once per day.
More bonus feats, Study abilities and Altered Script uses come one by one every two levels. The capstone at level 20 is a final Study ability.

In short the class features of the Archivist can be summed up as ‘Wizard, but Rune Casting’. Most of the build choices comes from what you want to do as caster, with each Design heaving its own specialization.

The dungeon has lines of meaningless text blocking some of the corridors. Anyone going over the lines is forced to make a Will save or temporary become unable to read, as well as losing 1d6 random Runic Charges.

Mirabelle Spellpage is a renowned siege weapon enchanter, and a secret cultist of a demon lord of forbidden knowledge who uses sacrifices to power her enchantments.

Runecharged Amulet, 250 gp.
This clay amulet is inscribed with runes and holds a single runic charge of a specific Design.
A Scribe can use this Runic Charge with any abilities that use runic charges or to overload a script.  The runic charge within the amulet does not count against its users normal maximum of runic charges he can maintain at once based on his scribe level.
The scribe still cannot overload more charges into a given script than his normal maximum. If he has more runic charges available than his normal maximum, he chooses which of the ones available to him are overloaded into the script. He does not have to use the charge in the amulet if does not wish to, but must otherwise overload as many charges he can as normal.
To randomly determine what runic charge design is in the amulet, roll on the following table:
d% Charge Type
01–16 Alteration
17–33 Creation
34–50 Destruction
51–67 Invocation
68–84 Manipulation
85–100 Revelation