"Well the most relevant thing is that he's like 600 years old. Supposedly--I haven't personally confirmed any of this--he's approximately the greatest alchemist ever and he successfully created a Philosopher's Stone, which is a magic doodad which can turn other things permanently into gold and dispense Elixir of Life. He's definitely actually that old, I've checked, but I haven't been able to confirm that the Stone exists and does what it's supposed to do. He'd better cough up whatever secret he's got that's keeping him alive, though, if he wants what I've got to bribe him with." 

"...and what have you got to bribe him with?"

"Ancient lost magical lore!"

"Well, you'd have me sold if I were Nicolas Flamel. But I'm not six hundred years old and I can't offer you the secret of immortality." The conversation has perked her up some; she stretches slightly in her chair. "What are your thoughts on dinner? I'm thinking we should probably go together when we do, for safety's sake."

"Sounds like a plan. I'm not actively hungry yet but I could eat."

"I'm famished, I had a bit of a packing marathon to get all this," she waves vaguely at the desk as she stands, "loaded up for transport. Shall we?"

"Let's!" 

Angelica gets up from her desk and stretches and moves towards the door. 

Ellen, moving somewhat more stiffly, takes rearguard.

As they approach the door, her hand lands on the back of Angelica's neck, and all of a sudden everything's coming up tentacles. Red-black tendrils expand from the point of contact, rapidly enough to cover her body in mere moments.

Angelica has very good reflexes. 

Her wand is out of her sleeve and in her hand in less than a second, and less than a second after that it's pointed behind her. 

"Imperio."

Just as they were beginning to contract, the tentacles go limp.

What was previously a normal-looking human body is now an amorphous mass of writhing red-black flesh-snakes with vaguely the right silhouette for a human form. They're still moving, but much slower now, all the ones all over Angelica crawling listlessly back into the main mass while the ones composing the main mass just sort of undulate in place.

She'd been hoping she wouldn't have to do this, but it does make things simpler, in a way. 

Return to your humanoid form, she instructs her roommate through the curse. 

Slllllurp go the tentacles, and once they're all in place, they smooth themselves together and near-instantaneously wrap themselves in skin and clothing to look just like Ellen did before Surprise Tentacle Time.

Tell me what you were trying.

"I was trying to give you immortality," she says, smiling slightly.

Tell me why you felt the need to wait until my back was turned to do it.

"I assumed that you'd turn me down if I offered to consume your body with my virus tentacles and make you a part of me, because you seem like a basically reasonable person," she says. That's definitely an amused smile on her face. "And I didn't want to reveal that I was more than human before I had you, because trusting my roommate at Mind Control University on the strength of one pleasant conversation would be a terrible idea."

"You're right! I would turn you down," she agrees brightly. "And now I know that I can't trust you, although the conversation was quite pleasant. If it makes you feel better, I definitely wasn't going to strike first. Do you currently have any mind-control capabilities besides the virus tentacles?"

"Not yet," she says, still smiling. "Honestly, I think you should give the virus tentacles a chance. They're friendlier than they look."

"The problem is that I rather suspect that if I tried them and didn't like them I would be pretty well stuck. How thin can you make them?"

"I'm sure someone could figure out a way to extract you if you really wanted. Why do you ask?"

"I want to know if they could potentially penetrate a ward designed to keep out solid matter but let air exchange freely."

"I'd imagine not. I have to get up close and personal to take someone, anyway, and ideally catch them while they're not paying attention. If I snuck a few little tendrils past your wards while you were sleeping—I assume that's what you're getting at—the most I could do with them would be tickle you." She smiles again. "No, really, though, don't you want to hear my pitch for why you should let me assimilate you?"

"Sure, gimme the pitch."

"I have no interest in controlling you for its own sake; I only want to make sure of my own safety. If I take you, I'll reconstruct your body and pretty much send you about your business as normal, except that you'll have a copy of me watching your every move from the inside, making sure that you don't betray me and keeping an eye out for danger from other sources. The trick is, I've had this power for over a year, and I can make multiple copies of one individual if I have enough biomass, plus I can share around my library of copied people by having one of me split off a duplicate of herself for another one to consume. So if I get to consume you once, then I can recreate you at home even if the copy of you attending this school goes back to your world and dies there. You get to have backups of yourself, for as long as the network of Ellens persists, which will be indefinitely if I have anything to say about it."

"Surprisingly compelling," she admits, "but the answer is still no until and unless I can be absolutely certain that any me-copies you produce will still have my magic. And even then I'd have to think about it."