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We all know that a really messed up rules situation must involve a Humility. So here we go.

This site discusses the scenario when an Urborg, Tomb of Yawgmoth becomes animated (e.g. via Nissa, Worldwaker), while a Humility is on the board.

The author of the mentioned article comes to the conclusion that all lands are now swamps, yet Urborg itself cannot be tapped for mana, since it has lost all its abilities to Humility.

What I don't understand is: Urborg looses its rules text saying that each land is now also a Swamp. So why do the lands continue to be Swamps? Would they loose their Swamp type if Urborg left play?

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3 Answers 3

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The lands continue to be Swamps because of the layer system. The layer system, described in section 613 of the comprehensive rules, is one of the most complex parts of the rules to understand and remember correctly. But basically, what it says is that when multiple continuous effects are being applied, (Such as Urborg's effect and Humility's effect), there is an order in which the different types of effects are applied.

Urborg's effect, as a Type-Changing Effect, is applied in layer 4. After it has been applied, (and all lands are now swamps in addition to their other types), layer 6 is applied, which is Ability Adding or Removing Effects, including the effect from Humility that removes the ability from animated Urborg.

Every time the game-state changes, these layers are re-applied to get the new current state of things. But whenever they are re-applied, Urborg's effect is applied before Humility's effect.

And yes, if Urborg left play, then the layers would be re-applied, and now there is nothing to change the lands into Swamps, so they would lose their Swamp type.

There is a good explanation of the layer system here.

I think an important key to understanding this is realizing that it's not so much that the other lands "lose their Swamp type" when Urborg leaves play (or when Urborg loses it's ability). Rather, it's that whenever the game-state changes, everything is re-evaluated, starting from what's printed on the card and adding the layers one at a time. So as opposed to the lands "losing" the Swamp type, they simply no longer have it added again.

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Thanks. The fact that everything is re-applied whenever the game-state changes answers the question to me. And now it all makes sense (I guess). –  john_leo Aug 12 at 15:32
    
@john_leo I asked a similar question before: boardgames.stackexchange.com/questions/14520/…. The answer also turned out to be because everything is removed and re-applied. –  GendoIkari Aug 12 at 15:49
    
Interesting. I didn't know that Volrath's Shapeshifter is such a big rules' mess. –  john_leo Aug 12 at 16:31

You are asking about the interaction of two Continuous Effects. The rules covering this are found in aptly named CR 613, "Interaction of Continuous Effects". It documents that continuous effects are continually reapplied in layers.

613.1d Layer 4: Type-changing effects are applied. These include effects that change an object’s card type, subtype, and/or supertype.

613.1f Layer 6: Ability-adding effects, ability-removing effects, and effects that say an object can’t have an ability are applied.

The effect from Urborg's ability and Nissa's ability are type-changing effect.

The effect from Humility's ability removes abilities.

As such, Nissa animates Urborg and Urborg makes each land a Swamp (in addition to its other types) before Humility removes the abilities.

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From the rulings on Urbog from the page you linked to:

If Urborg loses its abilities (for example, it becomes a creature and then Ovinize is cast on it), all lands on the battlefield, including Urborg, will still be Swamps, but Urborg won't have the ability "Each land is a Swamp in addition to its other land types." Urborg also won't be able to tap to produce {B}, but other lands (including those that enter the battlefield later in the turn) will. The way continuous effects work, Urborg's type-changing ability is applied before Ovinize removes both the type-changing ability and its own mana ability.

So the issue is the order in which continuous abilities apply, which is the Layers system in M:TG. Type defining abilities apply in the layer 4 while loses-all-abilities is in layer 6.Article Explaining layers

This means that your process layer 4 first, giving all lands the swamp type. Then you process layer 5 (colour changing effects). Then layer 6 where all creatures become 1/1 and lose all their abilities. Since the type change happened in layer 4, all lands are now swamps.

If Urborg leaves play, then it will no longer be applying the Swap type in layer 4, and so lands will lose their extra swamp type.

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Thanks, I understood that part. My problem was that I didn't understand why the other lands continued to stay swamps once Urborg lost its respective rules text. –  john_leo Aug 12 at 15:36

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