Dominant Ti: Magnussen collects and analyses information, and refers to his process of reviewing information as “reading.” He needs a way to organize information, thus the “mind palace” (my theory is that he has a photographic memory, but uses a memory palace in addition in order to organize his thoughts). Magnussen gives extremely short answers for everything, not giving out any information until he knows the people he’s giving it to will die before they can share it. He gets annoyed with Sherlock for asking questions, and tends to put them aside so that he can devote his energy to analyzing. He is perfectly capable of setting aside emotions in order to accomplish things. He doesn’t really plan ahead at all, but simply uses information to manipulate his environment in the here and now.
Auxiliary Ne: Magnussen easily recognizes connections between different bits of information, and quickly picks up on other people’s emotions. He has an emotional “pressure point” set for everyone, which he exploits to get them to do his bidding. He gets annoyed when Sherlock runs off on tangents, but prefers to stick to one idea at a time. He has no evil plan, but thrives simply off of making other people’s lives chaos and hell. He intuitively sees emotional connections between people, and recognizes possible ways to tear those connections down.
Tertiary Si: Magnussen has a much more powerful memory palace than Sherlock does, likely more of a photographic memory than an actual memory palace (at least that’s my theory – being a memory palace user myself, I doubt it possible to actually reach the extent that Magnussen supposedly does). That said, he almost doesn’t have a true method for remembering things –he just remembers them. Magnussen uses his vast store of knowledge to blackmail and manipulate people into giving him the ultimate power that he wants. Magnussen values tradition and order (though he derives order in his own affairs by creating chaos in other people’s). His house is classy and his attire always fresh.
Inferior Fe: Magnussen can read other people’s feelings like a book. He is loyal to no one and doesn’t care whether he hurts other people’s feelings (just so long as he gets his way). His time is extremely important to him, so he gets impatient when he feels like Sherlock is wasting his time. His feelings are mystically invisible on the surface, and his face typically assumes a dead-eyed stare. However, it’s safe to presume that most of his actions, though carried out through logic, are motivated by his feelings.