Fey Caller Unchained Summoner Archetype
is OK, but it does something interesting to normal Unchained Summoners
Fey eidolons don’t have alignment subtypes.
This implies no-archetype UC Eidolons normally have alignment subtypes. This doesn't normally do much except make them vulnerable to Favored Enemy (Meh, when's the last time you fought an enemy ranger with FE: Good Outsider?) but Book of the Damned has several feats that requires at being an Outsider with the Evil subtype, normally off limits to PCs. Less ambiguously the Nightmare Chain feat is legal for Eidolon of the Kyton subtype (I'm sure it's a different Kyton subtype than they intended, but it is a kyton subtype). This is a pretty good option for natural attacks, giving two chain attacks that do 2d4 damage (really good when size increases are involved) with 20 foot inclusive reach)
Also on the topic of Eidolon feats, the Damnation feats are pretty decent, but have the huge drawback of damning your soul. Not an issue with an Eidolon. With the Ancestor subtype the fluff could even be the Eidolon is normally in Hell.
edit: Just realized Evolve Companion doesn't have the maximum number of attacks restrictions an actual Eidolon does, nor does it have subtype restrictions.
edit: Rod of Absorption
: Holy ****! Lets you use 50 levels of spells without expending a slot. Needs charging, but the charges never appear to vanish and only counts total levels and explicitly allows SLAs, so any cheap magic item with an at-will SLA can fill it in at most 5 minutes. 9th level pearls of power are reusable, but this doesn't take an action to recharge your slots. If you want to nova as a high level caster, here you go.
edit: Burdened Thoughts
completely disables flying with just a will save. If that wasn't good enough it encumbers the enemy and might stagger it.
edit: Just started looking at the Mesmerist more in depth. Found Devilbane Impediment. Forces all enemies hit by your stare to make a concentraction check (15+spell level) and if the enemy is an outsider, "double the hypnotic stare penalty applied by the devilbane gaze improvement (but not the Will save penalty the original hypnotic stare imposes).". How this is doubled is unclear (multiply the check DC by 2? make two checks and fail if either fails? 15+double spell level?) but this is great hoser design: Useful against something pretty common (monsters with SLAs) and really good against one uncommon but hardly rare thing (and it could be common in some campaigns.) Note that SLA users, unlike real casters, often don't have that high an ability score and outsiders tend to be the ones that do have decent scores.
Edit: New officially licensed PF1E book Niobe. Not third party under the compatibility license, but actually licensed with the PF name. Best comparison is, ironically, Dragon Compendium.
There's a new class Omdura. Mid BAB caster with charisma based spontaneous 6th level spells from Cleric+inquisitor list and some battle priest abilities. Nothing great, but if Inquisitor with its limited spell list is tier 3, so is this with its strictly better one. Frankly a warpriest archetype swaping the spellcasting from wisdom based prepared to charisma based spontaneous with the inquisitor's list would have done everything this does better.
The real gem is Blessed by a god or Dragon
, which lets you cast a spell from the cleric list, as though you were a cleric of your level, once per day or as a swift action with a one month cooldown. Very easy to qualify for: 7th level and a feat with no requirements but 5th level. At worst
this is a way to grab condition removal.
Edit: Sleeping on it, uses I thought up for the feat:
Using it on a Wizard gives all cleric spells for crafting.
There's at least one prestige class (Dawnflower Dissident) that requires divine casting to enter but can advance any casting. That one class is hardly amazing, but there may be more content like that.
The wording isn't clear (the crunch of this book is terribly edited from what I've read), but this may make the casting time exactly ten minutes. There's a handful of spells with longer casting times. Of Cleric spells, Ritual (made an NPC spell by its 8 hour casting time) and Scrying are the only ones I can find that this would be all that useful for (doesn't need an expensive component, isn't super niche)
Overall this feat is good, but not broken. You may
need to meet the minimum wisdom to actually cast spells with this, which greatly diminishes it.