Player A controls Urborg, Tomb of Yawgmoth and Plains. Player B controls Blood Moon. I know that Urborg is a basic Mountain with no abilities, but my question is: What is the text of the Plains controlled by Player A? Gatherer rulings would have me believe that the Plains is a functional Scrubland, but I'm not 100% sure.

Thanks.

Hello,

No it does not. Urborg's effect is dependent on Blood Moon's effect, since applying Blood Moon's effect will change the existence of Urborg's effect (by removing its abilities when it becomes a Mountain). You apply Blood Moon's effect first, and nonbasic lands become Mountains. This removes Urborg's ability and it only has the ability to tap for one red mana. Since Urborg no longer has any abilities, no lands will gain the Swamp subtype. Your Plains is just a Plains: it will not have the ability to tap for black mana.

Nathan Long
Magic Rules NetRep