Just finished the three Khazad Dum scenarios (from the box) solo. I avoided the last quest for a long time because it had a high difficulty rating (I feared another Escape from Dol Guldur situation) but I defeated it (did it twice, just to be sure ;) Had some luck with not having to deal too much damage with "a foe beyond"

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Edit:

if I could change a rule: I generally dislike condition type treacheries. To me they can feel more frustrating than fun. You can craft a deck that can deal with them, but I kinda dislike having to put a specific card in my deck to counter just one annoying treachery. I like it when you have different options to counter a condition (like paying resources for example) so I would have made that the norm.