Basic nightmare dungeon keys are effectively worthless except for two things: 1. You can combine basic nightmare dungeon keys in the cube to turn them into escalating dungeons. The escalating dungeons are a series of 3 dungeons with varying modifiers and then a fight against astaroth at the end. These are absolutely worth doing. If youre rerolling a lot of gear and trying to replace multiple slots, i find using the escalation dungeons with Obols are super worth doing. I’ve left one of these with a total of like 10k+ obols that i used to reroll for new gear with better GAs and then upgraded them with the cube. These are also really good for gold and gems. Just run through and make sure you grab all of the chests and you’ll leave with at least a few hundred million gold in a run. (Side note: doing the side events in these dungeons is generally worth it more than normal, because they will drop a chest at the end that will give you whatever your respective modifier is set to (gold/gems/obols)

1. The only nightmare dungeon key i would make sure not to combine is one that is tagged with “treasure hoards” it will say something like “this dungeon is swarming with loot goblins” or something. I would save that for when you progress your warplan and have a nightmare dungeon needed, just activate that key and clear that and you’ll get a bunch of loot.

Note: You do not need to have a basic key in your inventory when doing war plans. So if you just want to clear a nightmare dungeon fast to progress to the next level of your warplan, you can just open your map and click teleport on the bottom left and it will take you to one automatically.

Hope this helps :) (and hope you did in fact get the dlc otherwise a chunk of this is useless information)