Honestly not much. Both have a short quest associated to them and the result is an additional puppet. But considering that you can only choose 2 puppets to go with your Demon + main char, it seems kinda redundant. It can open up some new playstyles but there is already an overabundance of puppets in the game.
Other than the new characters, you are not missing out on anything important. The Chromaton Chronicles at least has some context but Necrophage just randomly sends you into some dungeon without any explanation whatsoever. Both DLCs consist of a small area from which you have you backtrack to previously visited areas to hunt down a few newly spawned quest monsters. You come back, use the items you got from them, fight a boss and that's pretty much it. Takes like 30 minutes for each.
Post edited December 22, 2020 by idbeholdME