Comprehensive Rules Changes
This rule was very slightly rewritten to clarify that a spell or ability that lets you choose zero targets still "requires targets." The requirement in this case is saying "nah, I'm good." This clerical change doesn't matter for anything until (spoiler alert) you get down to the 605.1 rule change.
I added an addendum to the list of ability words.
603.3c and 700.2b
These rules handle modal triggered abilities where you go to put the trigger on the stack but you just can't choose any legal modes. They talk about if you "can't" choose a mode, but lo! Ravager Wurm allows you to skip choosing modes! Now these rules say you yoink the trigger off the stack if no modes were chosen rather than if you couldn't choose one.
One of the requirements for an activated or triggered ability to be a mana ability is that it doesn't have a target. Priest of the Forgotten Gods does something heretofore never seen, perhaps due to the machinations of these forgotten gods: its ability produces mana and it has an optional target. The requirement for being a mana ability has changed to accommodate this by now caring about if the ability "requires" a target—and an ability that lets you choose no targets still counts as "requires targets" thanks to the previously mentioned change to 114.6.
This space was adept to adopt the rules for adapt, where the Simic's gimmick mimics monstrosity. If anyone is translating this article, I am so, so sorry.
I was contractually obligated to assign this spot to the Orzhov for the rules regarding their afterlife keyword.
And here I was obligated to—never mind, the Gruul set up camp for the riot keyword here, and I'm not going to get involved with that.
This is where the Rakdos put on their spectacle. Mind the puddles.