Goetic looks really cool.

Possessed Manifestation: As far as I can tell, this never says explicitly that a spliced goetic gets the horror's abilities. The Horrors section discusses them exclusively as distinct entities, and not as bundles of traits to be attached to a spliced goetic. I'd say the intent is clear (I'm guessing you wouldn't spend a lot of time fleshing out abilities that mostly only matter if the insane horror from out of space slips the leash), but it'd probably be worth making explicit just to save on silly arguments down the line. How long to horror effects last after a splice drops?

Psionic Flesh: I think most people aren't going to argue for 14 bonus hit points at level two (one per horror), but "each of the horrors’ ability score bonuses" is technically ambiguous as to whether it means "one at 2nd level, and every four levels there after" or "that, per horror". If the intent is that the horrors' ability score bonuses only count as feats while the goetic is manifesting them, language to that effect should be added (carefully phrased so that the goetic still counts as a psionic creature even while not manifesting, most likely).

Martyr's Consolation: When this says "Separate instances of this delayed damage do not stack: only the largest single instance of such damage is applied to Athanatism.", does that mean Anathanatism drops all but the highest split damage? This seems underwhelming compared to Martyr's Preparation until you get Mirror of the Soul...maybe because this mentions taking an effect for an ally, but not what happens in response to that. Without that, you get the ability to maybe tank some extra damage with a well-timed heal until 12th level, and then you can also potentially reduce the damage you take by your level. Martyr's Preparation gets to reduce damage taken by your level from the get-go, at the cost of requiring some good planning to get benefit from a heal. There's some good synergy with Destiny Bond and Guardian Stranger, though those come late, and are 1/day.

Martyr's Preparation: How long do the bonus points from healing last? Until it refreshes next round? Until they're expended? (ala temporary hit points)

Mirror of the Soul: Missed the "once per round, use one of its 1st level abilities as a free action" language from the other 12th level features.

Ancestral Guidance: This is a hilarious way to tank possession effects.

Clarisentience: Ironically, for "the most difficult horror to understand", granting a wisdom bonus makes it easier for the goetic to make Will saves and stay in control.

Look Forward: Describes Clarisentience as being the one to see the target's future, but the target gets the reroll effect. Should either change the language ("allows a creature it locks eyes with to observe the terrible consequences of its actions in the immediate future", also not a gaze attack), or allow Clarisentience to reroll a d20 that effects that creature (mirroring the effect of Gaze Backwards).

Gift of Vision: This is a really neat effect. All Seeing is pretty cool, too, but Gift of Vision is cooler.

Future Sight: Who is aware of the pseudo-turn? Also, "and it reverts back to its position and status prior to taking this pseudo-turn" could be cleaned up a little -- sort of sounds like you revert before taking the turn rather than afterwards.

Psychocreativity:
Astral Doppleganger: Should there be a restriction to having one construct out a time, or can a goetic with nothing else to do with their swifts have up to three by constantly refreshing them?

Zone of Shields: Missing "of" in "regardless its chosen..."

Psychokinesis: Does it's slam attack count as a weapon attack for the basic effect? Is it intended that psychokinesis keeps its powerful build ability while increasing to Large and Huge?

Telekinetic Limb: Can this wield a weapon? At what penalty?

Telekinetic Melee: Another cheesemonkey problem: how many weapons can you wield like this? Might be addressable by changing "its weapons" to "the weapons it is currently wielding".

Energy Arena: "Each of them rerolls initiative, and fights their own separate battle within the sphere." This needs some clean up. I'm also not sure why it's necessary to reroll initiative, especially if there's a chance that the goetic will need to drop the splice for whatever reason. How long does this last? Can it be dismissed?

Psychoportation: You missed editing out a reference to Scorn Earth in the second to last sentence of the second paragraph of the basic effect.

Tesseract/Impossible Step: one name is used in the header, and one at the start of its description.