Max!!

Threefold mind: Since altering the nature of his bond with Simon and Alvin, Theo’s mind has become host to a sort of triple consciousness. Simon and Alvin serve as secondary and tertiary awareness within Theo’s mind, as their physical bodies have effectively been fused in a more refined manner. The simplest way of explaining this is like having three different people observing the same events simultaneously. The things seen and heard will be slightly different for each individual but together they create a more complete picture. The inner voices can also confuse telepaths by talking over each other, making it harder to sift through and perfectly read thoughts.

Eldritch body: Simon and Alvin’s physical bodies have now been fused using Theo as the base since he was the host. For all intents and purposes Theo is no longer human, however he retains enough of his humanity that he’s also not a full eldritch being in spite of what his new powers make him out to be. Theo still remains the dominant mind and is therefore mentally still a human. His abilities are based on his original eldritch familiar Simon and are split into a more human form and a more eldritch form. Overall he’s still vulnerable to physical harm though he can heal from minor wounds within a few minutes. His reflexes have also become notably quicker, and can lift a small car. He’s still working on figuring out the full capabilities of both of these forms.

-More human: The only real initial sign that Theo's even changed at all is his left eye which is now red with black sclera. Theo now Has the ability to sprout up to six extra arms from his upper body. These arms are stronger than his human arms and extend down to the floor. From his lower back he can also grow up to eight tentacles. These extra limbs if severed simply retract and take up to 24 hours to regenerate. Similar to certain animals they will thrash about involuntarily for a few moments before effectively dying on their own.
-More eldritch: Theo becomes a tall imposing masked being in a long trench coat with no apparent limbs supporting him. Whatever is hidden within these garments is unknowable. True to his species whatever happens to be underneath can traumatize and/or break a person. He moves about like one would expect a ghost or a specter to move about likewise, chains clinking can also be heard when he does so. This form seems to be the other remnants of his original familiar, Simon however, it seems to be completely new. Theo’s scent is completely different when he is in this state. He cannot sprout limbs in this form, instead he possesses a pair of long barreled guns and generate several chains from beneath the coat. These chains can be used offensively to ensnare and flail or defensively by wrapping them around his body.