Trillochs: because your campaign really needed an incorporeal invisible chaos-aligned rage-controlling necromantic firefly.
Chassis-wise, they could be a lot worse. 8 outsider RHD are acceptable, the incorporeal subtype is nice, stats are okay (+6 con, +8 dex/wis/cha), DR 15/lawful is top-notch, 60 ft. blindsight is never bad, and 40 ft. fly is hardly terrible. Trillochs also possess innate invisibility, making them even harder to kill.
For all this defensive prowess, trillochs are very lacking offense-wise. In fact, they're basically useless there: they possess no natural attacks, spell-likes, or offensive abilities. Their closest thing to an in-combat option is inducing Rage (as the spell) on allied martials and enemy casters, or killing off dying foes with Death Knell (though note that it's non-friendly so y'know, maybe don't use it when allies are down). Class levels (warlock, binder, some caster maybe?) will somehow alleviate this passiveness, but even then it'll be struggling to participate meaningfully in-combat for the first few levels.
Honestly, I feel that while this concept is neat, it could've been handled a lot better by making the trilloch into an enchantment effect, or a natural hazard. As-written, trillochs are meant to be some kind of force-amplifying, nearly undestroyable support, but fact is that a creature that essentially can't be destroyed and can't directly affect PCs is more likely to cause frustration than enjoyment.
As a PC, the trilloch is... tough to rate. However, it's lack of easy communication, tool use, weapon use, interaction with the physical environment, ability to contribute meaningfully to combat, and advancement options mean I'm forced to assign a -0 here. You could play as a trilloch, and maybe have fun doing it too, but there's simply better options out there.