Urborg and B Moon

[Mattao19]

{Urborg Tomb of Yawgmoth} vs {Blood Moon}

BM wins right?

[rarehuntertay]

4/1/2008: If Urborg, Tomb of Yawgmoth and either Blood Moon or Magus of the Moon are on the battlefield, all nonbasic lands will be Mountains, not Swamps. Urborg, Tomb of Yawgmoth will be a Mountain as well. It will have "{T}: Add {R} to your mana pool" and no other abilities.

[Remillo]

To go a little more in-depth, we call this idea "Dependency".  Both abilities apply in the same layer (Layer 4), so they should be applied in Time-Stamp order, right?  Well, we have to look at what the abilities do.  Urborg adds an additional type to all lands, but Blood Moon turns all Non-Basic lands in to Mountains (and lose all of their abilities).  Because Urborg's ability existing is dependent on whether or not Blood Moon is on the battlefield, we simply don't apply the ability at all while Blood Moon is on the field.

In short: Blood Moon and Urborg, regardless of Time Stamps, cause all Non-Basics to just be Mountains, and Basics are not Swamps in addition to their other types.

Because a thing called Dependency.