Someone should steal his house.
MAGNUS: Well, thanks, sport. There's a spell for damn near everything. I am impressed, though. You did exactly what you should've done. Though I am gonna miss those two from my zoo. Oh, gentlemen, you are in the midst of the greatest collection of supernatural rarities and antiquities on the planet. I'm sorry. Did you say that you were Men of Letters? I thought that whole thing died out after '58.
Also, damn you Henry. You really were the stupidest smart man alive. Love how Magnus is like, part-teacher, part-crossroads demon, part-King of Hell here.
MAGNUS: Hunters? Wow! Hunters. With the key to the kingdom! The boys must be spinning in their graves. Damn snobs. Bunch of librarians, if you ask me. Although I was always fond of Henry. I was his mentor, you know? Yeah, till the squares gave me the boot. Yeah. 'Course, he came here to visit me, in secret. Called out to me, same as you did. Oh, yes. Quite the wild hair, your grandfather was. Things never change, do they? I kept telling the boys over and over again -- I would say, "we could stop all this. We could rid the world of monsters once and for all if we just put our minds to it", but, "oh, no," they said.
And yet, for all that wanting to solve everything, he drifted so far into "the ends justify the means." And that turned him into a king of a prison, sort of Chuck-like. Another real creepy elements to Magnus. He has the WORST parts of everyone.
MAGNUS: One little design flaw to the place -- no windows, no doors. DEAN [drawing a machete]: Well, in that case... I'll just make my own. MAGNUS (wins easily): Welcome to the collection, Dean.
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But most importantly, I wish they'd kept his house.
Like, maybe they lost access right after they left it or maybe they had a key that didn't work when they went back to it. But. Hell of a Safehouse, ykwim? It would have torn both Sam AND Crowley apart to have to lose that, or it it dissolved behind them.
I assume they killed his zoo in the initial attack, but have a hard time thinking Sam wouldn't try his damnendest to come back and loot all those objects.
EDIT: God, I'm glad he never got his hands on Rowena. How HORRIBLE it would have been. MoL tended to hate witches anyway, but he'd be so greedy to tear her secrets out if she refused to give them.