After completing the Dispenser script which shoots mobs, potions and a whole lot of other things when triggered I confirmed the working of Custom items within dispensers. This is how it works:
Custom Items can be created within Denizen, just like you have i@stone I could create i@SuperAwesomeStone and add super awesome effect on that stone.
What I did is create such a item called i@AncientDungeonArrow. And will place these arrows inside a dispenser. If a dispenser has this item and is not placed by a player it will shoot off all sort of things.
So, what if I make a script that spawns herobrine upon triggering the dispenser? Tadaa! You'll have yourself a Boss walking around ( With custom attacks, custom loot and mooree! )
Here´s a boss example: ( OOOllldd Screenshot though )
Haha, Old memories coming up... This herobrine is actually scary once you meet him. Trust me
Note: If you have or are planning to buy NLBlackEagle's Realm and would like a certain custom boss to be implemented, tell me about it and I'll may include it into one of the possibile dungeon bosses!