104.2a, 304.5, 307.5, 603.2a, 701.13c, 702.7c, 810.8a
Whoa, so many rules changing with one topic—this must be a big important one! Nope. This one's purely editorial. These rules used the word "prevent" colloquially, but "prevent" is a load-bearing word in Magic, referring to prevention effects. The colloquial meaning here is just close enough to the "prevention effect" meaning as to be uncanny and make you wonder whether it has hidden significance. These rules now use other words, mostly "preclude," to avoid stepping on that. This looks like a big change, but it's not a functional change at all.
This rule talks about gaining and losing abilities. I've broken it up into bite-sized sub-rules and, as icing on the mini-cupcakes, added a sub-rule that more clearly handles how Mairsil, the Pretender's ability works.
This rule assures you that even though "draw three cards" is processed as "draw draw draw," the instruction to draw three can be modified before modifying individual draws. Alms Collector finds this purrfectly helpful and baps the existing 120.2a down a couple letters.
While I was modifying card-draw rules, I added one that clarifies how Spirit of the Labyrinth interacts with costs and effects of drawing multiple cards. To wit: If you're told to draw two cards, you draw one, but if you're given an option to draw two cards, you can't choose to. This matches how you handle "sacrifice two creatures" when you can sacrifice only one.
I buried Treasure in the artifact subtype list. You'll never find it.
Huatli joins the list of planeswalker subtypes. This rule also lost a paragraph about the Planeswalker Uniqueness Rule, which is no longer a thing.
This is the best rules change—it's the list of creature types. And, I'm proud and excited to announce, it has a new member:
Oh, and also Dinosaur, I guess.
Ability words have no meaning, but they're documented here. Eminence and enrage are both on the list now. In that order, even. How convenient!
This is where the Planeswalker Uniqueness Rule would be if I had one. But it's gone. All planeswalkers are now legendary! The real fun is way down in 704.5j, which was the rule describing the state-based action of the Planeswalker Uniqueness Rule. That's awfully early in the list of state-based actions, so when I removed it, a lot of rules had to be renumbered and every reference to those rules had to be updated.
These rules discuss combat requirements, and it has a small change as previously noted in this article's future. There's a new line noting that if a creature is forced to attack or block in any given turn, such as "this turn," it must do so every time it's able to during that turn.
This rule discusses attack triggers. It parallels the section on block triggers down in 509, adding some content that was obvious and some new phrases, but nothing here is a change from previous rules.
508.5, 802.2a, 805.10e
These rules described the defending player as the one the attacking creature attacked. Thanks to Portal Mage, that isn't always true anymore! These rules are updated to make "defending player" really look at the player that's currently being attacked by that creature. It's a lot wordier, but that's the price we pay for the triumph of Portal Mage.
We've had lots of cards check which creatures are attacking players, but which players are attacking or did attack another player is a new one. This rule defines how to interpret that.
And rounding out our tour de force of section 508 updates, this rule handles reselecting who or what a creature is attacking. Between Portal Mage; the Curses; and O-Kagachi, Vengeful Kami, this edition of Commander will always be Commander 508 in my heart.
This is the rule about block triggers I mentioned up there in 508.3's changes. While I was revisiting how we express the generic trigger conditions for attack triggers, I hit upon a phrasing that was more generic and applied it to this rule's sub-rules, too. It's not a functional change in any way.
Caged Sun has an unusual ability. It triggers whenever a land's ability adds mana, not just when a land's mana ability adds mana. Rather than let this ability sometimes be a mana ability and sometimes not, the rules have been adapted to make sure it's always a mana ability.
This one's weird, so buckle up. This rule handles how we process enters-the-battlefield replacements. It started out simple, but grew exceptions over time. It led to natural results in many cases, but one kept causing plenty of confusion: how continuous effects interacted with the replacement effects.
Blood Moon and Dimir Aqueduct together illustrate the confusion nicely. This rule said that you ignore Blood Moon to determine that Dimir Aqueduct entered tapped, but then it loses all of its abilities and doesn't trigger. Players learned that specific interaction since Blood Moon saw plenty of play, but then every time an identical situation would come up with new cards, they had the exact same confusion. That's a good sign that players are learning an interaction rather than a rules system. That isn't necessarily an awful thing, but it starts to get problematic when that interaction isn't an edge case anymore.
Arcane Adaptation and Metallic Mimic make things weirder, and they're in Standard together pointing to tribal happiness. If your Metallic Mimic is fond of Ferrets (and come on, who wouldn't be?), you have Arcane Adaptation making everything you own into a Ferret (okay, that must smell awful), and then you cast a Jellyfish, you have a Jellyfish Ferret spell on the stack. You control a Jellyfish Ferret when it enters the battlefield. But it wouldn't get a counter from Metallic Mimic because of how this rule worked.
So this rule's changing. Now, to determine what replacement effects will apply to a permanent entering the battlefield, you look at continuous effects that modify that permanent's characteristics coming from the permanent itself along with those that already exist and will affect that permanent. Dimir Aqueduct enters the battlefield untapped under Blood Moon. Humility causes creatures with modular to enter without their +1/+1 counters. Metallic Mimic can distribute +1/+1 counters happily to your army of Ferrets under Arcane Adaptation.
614.16d, the parallel rule about "can't" effects, also gets to go along for the ride, even though this rule hadn't hit the "no longer an edge case" threshold yet. It also got a +1 and became 614.17d when you see the new document.
Is this new system perfect? Probably not. But it results in players being able to guess an answer that matches the correct answer more often.
This new rule hops in and bumps the existing 614.16 down. The new rule establishes that when a replacement effect watches for "an effect" creating a token or putting counters, it'll do its thing if a replacement effect or prevention effect causes these things to happen. This covers some weird cases where Doubling Season may or may not double the counters and tokens.
I cut down some brush and just happened to find rules for explore!
702.25k, 110.5f, 704.5d
Once upon a time, phasing moved objects to the phased-out zone. This zone change was treated as not really a zone change by everything, so with the Magic 2010 rules changes, phasing was made to not actually be a zone change anymore; phased-out things just pretend they don't exist. Tokens still actually ceased to exist because that's how it had worked, but it led to some weirdness, like Batterskulls stuck forever in limbo. Teferi's Protection brings phasing back for a one-time appearance, and it does so in a token-heavy deck, so we agreed it was time to clean up this quirk in the rules and let tokens survive their journey through phased-out status.
Monstrosity has a rule to link "monstrosity X" to abilities that trigger when the creature becomes monstrous. Morph didn't have a similar rule linking X in a morph cost with abilities that trigger when the creature turns face up. No one was ever actually confused by this, but now there's a rule that says it works.
These rules talk about double-faced card icons. Welcome to the list, Compass Rose and Land Icon!
Explore is the only addition to the glossary this time.