Comprehensive Rules Changes
This rule has two children rules that used "became the target" to mean "was chosen as the target." This conflicts with how we normally use "become"—in Magic, something can't "become" something if it already is that something before something else somethings the something something. (The term for what you're experiencing now is semantic satiation.) I updated these rules to say something more like what they mean. Or something.
Previously, this rule claimed that alternative costs were always optional. You may remember this little-known ability called "flashback" from back in 2001 that is an alternative cost and is definitely not optional. Has anyone ever said "I'll flashback Firebolt, and because alternative costs are optional, I'll pay R instead of 4R"? This rule is really saying "Just because you may pitch a card and pay life for Force of Will doesn't mean you can't just choose to just pay all that mana." I've adjusted it to sound more descriptive than prescriptive and to be truthier in its descriptiveness.
Here's where we say that drawing cards in a shared-team-turns game has players draw the cards in any order they'd like. I've changed the word "effect" to "rule or effect" so that your team's draws for the turn are properly handled.
God-Eternal Kefnet lets you reveal a card as you draw it, just like the miracle keyword. For miracle, it was obvious that you could look before choosing because how else would it even work, but for Kefnet, it was less obvious. This new rule makes it clear that you get to look before deciding and incidentally supports miracle.
The rule about moving counters was written a little too narrowly. In another instance of updating a rule to say what it means, I've updated this rule to more accurately cover what it's trying to say: if it's not legal to both remove a counter and to put a counter, moving a counter isn't legal.
The list of planeswalker types is updated for our four new planeswalkers! Welcome Davriel, Kasmina, Teyo, and
Where does Bolas keep his Armies? No, not in his sleevies. He keeps them here in rule 205.3m, the creature type list! I mean look at him, he is a Dragon, he isn't even wearing a shirt or anything with sleeves.
This is the rule that says a delayed triggered ability normally triggers only once, the next time its condition is met. So, what happens if Ugin, the Ineffable made two tokens thanks to Doubling Season and then they both die at the same time? Which death causes the ability to trigger? Now there's an answer: the trigger's controller chooses.
The 612 section of the rules is a dusty corner where text-changing effects lie. I've thrown a new rule in to cover Awakening of Vitu-Ghazi's name-changing effect, so now we can go back to not looking at this section of the rules for a few years.
After you choose to show off a card for God-Eternal Kefnet and its ability triggers, what happens to that card? With no rule saying otherwise, it sure sounds like you get to just hide it again, but you're going to copy it and its characteristics are kind of important. Do you have to show it to your opponent after the ability's triggered but before it finishes doing its thing? Nothing says so. Rather than make players go to Oracle to find out what the card did, we're saying so: if revealing a card makes something trigger, keep that card revealed until you're done with the trigger.
The rules for proliferate got a makeover! The rule reminding you who chooses counters is dropped, since there are no more choices on the counters, and the other two rules are updated to match the new reality.
I gathered the rules for amass here. They're assembled neatly in rank and file.
Rivals of Ixalan joins Ixalan on the list of double-faced cards' face symbols. There's an open question of whether we just drop this list the next time we have double-faced cards; it's getting long and weird.