418.5c An effect is said to “depend on” another if (a) it’s applied in the same layer (and, if applicable, sublayer) as the other effect (see rule 418.5a); (b) applying the other would change the text or the existence of the first effect, what it applies to, or what it does to any of the things it applies to; and (c) neither effect is from a characteristic-defining ability. Otherwise, the effect is considered to be independent of the other effect.
418.5d An effect dependent on one or more other effects waits to apply until just after all of those effects have been applied. If multiple dependent effects would apply simultaneously in this way, they’re applied in “timestamp order” relative to each other. If several dependent effects form a dependency loop, then this rule is ignored and the effects in the dependency loop are applied in timestamp order.
Urborg doesn't apply its ability until the Blood Moon/Magus applies, and as such it's effect is negated. Basically, Magus/Moon > Urborg in all instances, since the Urborg is dependent on Blood Moon, the moon effect would have to be removed in order for it to function as normal.
