Doctor Doom doesn't care how many lands are discarded at the same time
As mentioned already, this card will also be available as a Full Art Version, so let us take a look at her Abilities
Its on a very cool card, lets be honest
Blood Moon says, Nonbasic lands are Mountains, whereas Urborg, Tomb of Yawgmoth says: Each land is a Swamp in addition to its other land types. The key difference here is the words in addition to. If you dont see this wording, like on Blood Moon, then the type change will overwrite whatever types the card had before
Whenever any creature becomes the target of a spell or ability, you can put a land card from the top of your library onto the battlefield , and if it's not a land, it goes to your hand