WOTC released a new Sage Advice document that clarifies a few things about the rules. Some early takeaways:
Magical Darkness: they clarify that magical darkness by itself is not impenetrable by Darkvision. if a spell or magical effect specifies that it blocks Darkvision (as is the case with the spell Darkness); then it does, otherwise it does not.
Multiple Dash actions: I don’t think we’ve been confused about this, but they make it clear that if a character gets, for example, the ability to Dash as a bonus action such as Lucretia’s Cunning Action or Kog’s Adrenaline Rush, you can still use your Action to Dash as well; meaning that a character could Move (up to their Speed), Dash as an Action and Dash as a Bonus action to yield Speed X3 in distance covered. Again, I think we’ve always played this way.
Opportunity attacks with reach weapons; if you are holding a weapon with reach (e.g. glaive or halberd) and a foe attempts to move out of your reach, you can use your reaction to attack; note that if you are using a reach weapon this only triggers if they try to move beyond your reach; a 5 foot move would not trigger your OA (though it would trigger any others adjacent not using reach weapons); good news, bad news. There used to be (in the 4e days, maybe even 3e?) an ability/feat called Threatening Reach that allowed you to make OA with reach; now anyone gets it.
Opportunity attacks and grapple, shove: yes, you can use grapple or shove as your OA rather than make a standard attack
Weapon Masteries
You probably noticed that I gave W.M. to the bad guys in our last fight. As I’ve mentioned, I want to stick to monsters from the 2024 Monster Manual for this campaign rather than tweaking them/making my own.
However I am interested in the W.M. effects. I think they are a pretty cool addition. When it comes to NPCs, especially “named” NPCs, I’ve been using DNDBeyond to create a character sheet (for instance, for Vindurain, the sorceress/warlock/witch). I am actually using an existing Monster Manual entry for The Gauntlet, because it’s good enough, but I gave him W.M. for his two weapons (longsword and javelin).
I guess that’s where I’m at right now; NPCs (versus “monsters”) may get the full character creation treatment; and thus have a full set of abilities, or they may be “monster” entries plus weapon masteries.
I may still explore the possibility of introducing some “monsters,” especially recurring ones, who might get a single W.M. with their “standard” weapon from the Monster Manual.