A dagannoth can be built in the Treasure Room of a player-owned house for 7,500,000 coins. They do not count toward a slayer task when killed. They are not common in a player owned house because they cannot range and are the same combat level as the Tok-Xil but cost 2,500,000 coins more. Despite this, their attacks are extremely accurate. Like most POH monsters they have been neglected to be updated graphically when their cousins in Waterbirth Island Dungeon and elsewhere were.
The update history project is a work-in-progress – not all updates to this topic may be covered below. See here for how to help out!