How about a thieving and summoning dungeon in runescape
Dungeoneering-style room with an obelisk in the middle, summoners walking about (could reuse forgotten mage or Taverley druid models, depending on lore). If you successfully pickpocket them you get (some of) the ingredients for a summoning pouch, if you fail they summon a familiar to attack you. Maybe, in addition to being able to defeat the familiar with combat, you could also attempt to banish it for a small amount of summoning xp.
Alternatively, Brassica Prime's cabbage knights. They could be bouncy cabbages with swords and shields. They could have taken over a resource dungeon to investigate the Daemonheim-style rapid farming patch there (they would have filled it with cabbage seeds, obviously).When defeated, they could drop as an untradable Blessed Cabbage, which can be eaten for a small heal and some rs gold. If you defeat and eat enough of the cabbages you earn the title ", the Cabbage Knight" (assuming it is not going to be available from the spring event - I don't think titles have been mentioned). I basically just want that title.
Also, a mining resource dungeon with a concentrated clay deposit near a deposit box. Possibly with gold rocks and sapphire rocks too, and a small furnace, so players can make bracelets of clay down there.