I think that the one-shot dungeons, not only Rattlebones, Zeus, Krokopatra and Meowiarty, but also Tanglewood Terror and Baddle of the Bands are very cool and enjoyable. Even though those already existing give some cool drops, i think we need more. Here are a few ideas:
1: A zodiac dungeon where you fight people similar to the celestians. You would then later actually fight the zodiacs themselves. The enemies can drop housing items based on the different zodiacs and perhaps even a zodiac-based mount, like a constellation dragon where it is made out of all the zodiac symbols.
2: A shadow-based dungeon. Only people who unlocked shadow spells and shadow pips may enter. You can get cool housing items and wands with a cool shadow effect, and there can be a dropped mount at the final boss that looks like your stuck in a huge swirling could of smoke, darkness and cinders.
3: A dungeon similar to Baddle of the Bands. Its where the wizard goes to a concert, but it turns out that it is a trap and the band members are Skurkis Screaming Moon (from Xibalba, Azteca), Pat Minotaur (Baddle of the Bands), and Kind Thermidor (Crab Alley), who are all being controlled by a master manipulator. The drops can be based on rock (Pat's style), pop (King Thermido's style), and screamo (or something like it; I'm pretty sure that is Skurkis's style). I also think it would be cool if there was a mount for it like a stego/avenging fossil except the plates are replaced by a dyable mohawk going down its spine and its kind of punk rock styled.
4: A mind-manipulation dungeon! It would have tons of puzzles, both physical and riddle. The story would be that the professors of Ravenwood are captured and held hostage in a house full of riddles. There would be bosses that would be spinoffs of the antagonists in the original 'Penny Dreadfuls', like The String of Pearls (The base for Sweeny Todd). The final boss would be Penny Dreadful herself, but she is being controlled by shadow rather than doing it of her own accord.
5: A Sweeny Todd based dungeon! I would love this, and the wizard would be coming for a haircut. She/He discovers the barber's plan and fights the spinoff based on him along with a spinoff of Ms. Lovett and Tobias. The dropped wands would be Sweeny's barber blades or Ms. Lovett's rolling pin.