Dungeons & Dragons has implemented a major change to how spellcasting NPCs and monsters are presented in statblocks. Yesterday during the Future of D&D panel at D&D Celebration, D&D Lead Rules Designer Jeremy Crawford noted that they would be changing how spellcasting monsters and NPCs were presented in its various rulebooks, using the upcoming book Mordenkainen Presents: Monsters of the Multiverse as an example. While creatures previously had spell slots and a full list of spells listed in their statblocks, the D&D design team will opt for a more streamlined approach that lists spellcasting as an action and features alternative attacks that replace damage-dealing spells.
The goal of these changes is to make these creatures easier to run as a DM by explicitly cutting down the need to research spells in advance of a session. Previously, a Dungeon Master would need to have their Player's Handbook handy to know a spell's exact rules, while other creatures had all their rules and abilities explained on the page. Additionally, players will now have the option of using damage dealing attacks instead of trying to cast spells, which can help improve a creature's damage in order to better reflect their Challenge Rating in combat.
These changes were actually implemented in the most recent adventure book The Wild Beyond the Witchlight. The three hags and other NPCs now have attacks that mimic certain damage-dealing spells. For instance, the spellcaster Kelek has the Sorcerer's Bolt attack - a melee/ranged spell attack that deals 2d12 damage on a hit. Kelek also has a Fiery Explosion attack that behaves similarly to an upcast Fireball spell, with players needing to make a DC 14 Dexterity Save to partially mitigate an explosion that deals 10d6. The Fiery Explosion now has a recharge feature instead of using a spell slot.
Other monsters and NPCs seen in more recent expansions and rulebooks will have their statblocks revised to reflect these changes in Mordenkainen Presents: Monsters of the Multiverse. This rulebook compiles updated versions of player options found in other books along with over 250 statblocks from various older rulebooks. Mordenkainen Presents: Monsters of the Multiverse will be released in January as part of an Expansion Rules Gift Set and then released later in 2022 as a standalone book.