When reading the new rules for the Alter of Despair, I noticed that they indicated that the new cards for the overlord should be shuffled into the deck from the Journeys in the Dark. Does this mean all the cards and monsters that came with the Well of Darkness expansion are not used in the Altar of Despair expansion? By this I mean do we remove the monsters, the overlord cards, the shop cards, the treasure cards, skill cards, power potions, the traps that were introduced in the Well of Darkness from this new expansion?

The Descent expansions are all designed to work even if they're the only expansion you have, so you could remove all your Well of Darkness stuff if you wanted. But I believe most people who own multiple expansions just combine everything.

Antistone said:

+1. The rules for AoD are written with the assumption that this is the only expansion you have. This is also why they re-explain the Treachery rules, in case you don't have WoD for reference.

If you want to combine both expansions at once, you can. Just add the AoD cards to the deck containing the base game and WoD card and you're good to go. As Antistone says, most people do this anyway.