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Spoilers for Commander 2018 have begun, and one card in particular has caught my attention:

Arixmethes, Slumbering Isle

This card is like no other I know. What may be truly interesting is how it interacts with the enchantment Blood Moon:

Blood Moon

Here's a blog post about this by a level 3 judge. I don't agree. How I see this interaction is as follows:

  • Blood Moon is on the battlefield. I cast Arixmethes.
  • Arixmethes resolves and enters the battlefield. As it must exist on the battlefield with at least one slumber counter in order to be a land, Blood Moon does not see it until after it has entered the battlefield as a land, tapped, and with five slumber counters. So far, I agree with the blog post.
  • Blood Moon finally recognizes Arixmethes as a nonbasic land. Arixmethes loses all subtypes and abilities and gains Mountain as a subtype (by Gatherer's second ruling on Blood Moon: "Nonbasic lands will lose any other land types and abilities they had.").
  • The effect that makes Arixmethes a land as long as it has a slumber counter is an ability (the example for rule 112.2a is very similar: "Example: '[This creature] can't block' is an ability."). This effect is therefore lost, and Arixmethes is no longer a land.
  • Immediately, Blood Moon begins ignoring Arixmethes. The ability that makes Arixmethes a land is regained, and Arixmethes becomes a land once more.
  • Repeat ad infinitum.

All of these happen too quickly for any player to do anything. The way I see it, Arixmethes and Blood Moon on the battlefield simultaneously will immediately end the game in a draw (unless, of course, Arixmethes has no counters).

Is there an error in my thinking?

  • 7
    In general, if you find yourself thinking that a ruling from a high-level judge is wrong, it's really worth digging into the rules to find out why they made that ruling. In this case, your question demonstrates that you were unaware of a large and important but obscure section of the rules that justifies the rulings. – murgatroid99 Jul 27 '18 at 17:46
  • Why do "Nonbasic lands will lose any other land types and abilities they had."? I understand why they lose other land types; but why would they lose abilities? Why would becoming a Mountain cause them to lose abilities? – GendoIkari Jul 27 '18 at 18:13
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    Because rule 305.7 says so. – murgatroid99 Jul 27 '18 at 18:17
  • @murgatroid99 Thanks. Not sure if I ever knew that rule; it's a surprising one for me. – GendoIkari Jul 27 '18 at 18:19
  • Losing other subtypes is actually a much more general thing, covered in rule 205.1a. – murgatroid99 Jul 27 '18 at 18:30
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The blog post is correct. What you're missing is the system that governs the order in which those effects are applied, commonly known as the "layer system", and officially known as Interaction of continuous effects

Put simply, the layer system creates a fixed order in which continuous effects apply to an objects, so there are no loops like you think you're seeing, and there is a single fixed answer to how any set of continuous effects apply to an object.

In this particular case, both of the effects modify the type of the object, so they both apply in the same layer. Then we have to consider timestamps and dependencies to determine the order in which to apply them. The relevant dependency rules say this:

  • 613.7. Within a layer or sublayer, determining which order effects are applied in is sometimes done using a dependency system. If a dependency exists, it will override the timestamp system.
    • 613.7a 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 rules 613.1 and 613.3); (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 or both effects are from characteristic-defining abilities. Otherwise, the effect is considered to be independent of the other effect.
    • 613.7b 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.

Before either effect is applied Blood Moon's effect has a dependency on Arixmethes' effect, because Arixmethes' effect changes what Blood Moon's effect applies to, specifically making it apply to Arixmethes. Arixmethes' effect does not depend on Blood Moon's effect, because applying Blood Moon's first will do nothing, because at that point in the evaluation, Arixmethes is not a land.

So, we apply Arixmethes' effect first, then Blood Moon's effect, and we end up with the result described in the linked blog post: Arixmethes is a Legendary Land - Mountain that can tap to add {R} with no other abilities.

  • This would be a dependency loop (613.7a-b), right? The dependency rule would then be ignored and stuff would happen in timestamp order, Blood Moon first and then Arixmethes, as I understand things. I still see no stable state. – Khuldraeseth na'Barya Jul 27 '18 at 17:59
  • OK, upon further examination, I think there is not actually a dependency relationship here. Rather, Blood Moon's effect simply doesn't apply until after Arixmethes' effect applies. – murgatroid99 Jul 27 '18 at 18:25
  • I guess the issue here is what happens when Arixmethes loses the ability that makes it a land. What's the key difference between Blood Moon taking this ability away and Naturalize destroying Awaken the Ancient? When the ability making the Mountain a creature disappears, the land reverts to its initial state. Why not Arixmethes? – Khuldraeseth na'Barya Jul 27 '18 at 18:42
  • In this situation, you're applying a single set of effects within a game state. One of those effects results in the ability disappearing, but it has already been applied, so that doesn't matter. If you Naturalize Awaken the Ancient, the game state changes, so you re-evaluate the continuous effects. – murgatroid99 Jul 27 '18 at 18:46
  • 4
    That might be a little misleading. The game state is constant at any specific time in the game. The layer rules simply define the order in which you evaluate effects to determine what the game state is. But each effect operates on a different partial computation of the game state based on applying the previous effects in the sequence. – murgatroid99 Jul 27 '18 at 22:13

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