The brain thing doesn't apply to his special talent. It's a part of his personality because when I made him I was going through a phase
Like he can make his thought appear, but in thought form. Imagine your could physically see a person's thought bubble. That's what he can do.
I think you missed a part. He can copy spells, but only when he sees them. And unless he's seen the spell, he can't use the spell. And on the emotions thing, I can't decide between a traumatic incident or an emotional meltdown.
Of course, he can mimic and use high-level spells, but he'll be more drained than an average unicorn casting it. And he can't use spells at all unless he's seen them a certain number of times.