Dungeons & Dragons received a lot of new content in 2021, but the old books are still being tweaked via errata, with many D&D monsters also being significantly changed. Along with the changes to the lore of the monsters in the Dungeons & Dragons multiverse, as well as changes to how enemies use spells against the party. The monsters in D&D are an important part of the game and they will likely continue to be changed in time for the upcoming 5.5 update of the game.
A new version of the stat boosts for the playable races in D&D was introduced in Tasha's Cauldron of Everything. These rules have since been used in books like Fizban's Treasury of Dragons. Wizards of the Coast wants to move away from pigeonholing characters into specific roles, simply due to their race. The people who are bold enough to become adventurers and risk their lives in a dungeon are extraordinary people and are not bound to the social norms of their culture. The new changes to the game have extended this line of thinking to monsters, as there shouldn't be a uniform rule for how every creature functions, as that would make the game boring. DMs are encouraged to use monsters in whatever way they'd like, without needing to be bound by pre-existing lore, though they are still free to use it if they choose.
Wizards of the Coast released a Sage Advice compendium at the end of 2021, which featured a lot of errata for D&D, including updates to spells. There were some books that received updates for the monsters and NPC villains that the players can face. Some of these involve lore changes, and some involve changes to their stats.
D&D's 2021 Monster Changes - Tree Blights, Strahd's Attacks, & More
The Curse of Strahd campaign received errata which brings it in line with the "Revamped" version of the book that was released in 2020. The Tree Blight monster has had its hit points reduced from 149 (13d12 + 65) to 92 (8d12 + 40). This is one of the boss monsters that players can fight in the adventure and it has been made a lot easier to defeat. Strahd himself has received some minor changes, as he can now perform unarmed attacks in his wolf form, and the damage type has changed from bludgeoning to slashing. The references to Esmerelda d'Avenir being ashamed of her prosthetic limb have been removed from the text.
D&D's 2021 Monster Changes - The Drow Player's Handbook Lore
The description of Dungeons & Dragons' drow race in the Player's Handbook has received errata, though their stats and abilities are the same. The text now says that drow have a shared heritage that links them to the Underdark and that some worship the evil goddess Lolth, but not all drow are evil. This change was made because the original description of the drow heavily referenced one part of drow culture from one setting, mainly the Menzoberranzan drow from the Forgotten Realms. The Menzoberranzan drow are heavily referenced in the popular Legend of Drizzt novel series, which is likely why they were used as the baseline at the start of fifth edition. The Forgotten Realms drow only encompasses a small part of the race from around the entire D&D multiverse, and the new description is meant to give a more general feel that makes it easier to use them in multiple settings.
D&D's Volo's Guide Lore Changed In 2021
The book that received the most errata was Volo's Guide to Monsters. The suggested alignments for the playable monster races have been scrapped, the lore removing some of the problematic elements of D&D's monsters has been removed, and some of the suggested personality traits for monsters are gone. The opening paragraph now states that the opinions presented within are from Volo's perspective, which is skewed, due to him being a traveler of the Forgotten Realms, and his views are limited to that setting. The developers later updated this errata, in order to explain some of the changes.
The suggested alignments were removed because most players ignored them anyway, as player characters often go against the grain and are extraordinary individuals, so the norms of society wouldn't apply to them. The lore changes were first mentioned back in 2020 and will likely be printed in some form in the upcoming Mordenkainen Presents: Multiverse of Monsters. The suggested personality traits removed elements that gave monsters cookie-cutter personalities, in order to let DMs know that they have room to experiment with races like beholders, gnolls, and mind flayers.
D&D's Spellcasters In Storm King's Thunder Were Changed
The Storm King's Thunder campaign has received a lot of errata. There are lore changes involving Dungeons & Dragons races like orcs, half-orcs, yakfolk, the Reghed clan, and the Uthgardt clan. These mostly tie into the lore issues mentioned above. The tressym is now classed as a monstrosity (it used to be beast) and now has any alignment, rather than Chaotic Neutral.
The biggest change involves the Spellcasting ability that some monsters possess. In the original document, creatures like Zephyros and Claugiyliamatar originally had spell levels with slots, and a list of spells for the DM to choose from. To use Zephyros as an example, along with his cantrips, he had four 1st level spell slots that could be used on charm person, comprehend languages, magic missile, or shield; three 2nd level spell slots that could be used on crown of madness, gust of wind, or levitate; three 3rd level spell slots that could be used on nondetection, protection from energy, or tongues; three 4th level D&D spell slots that could be used on conjure minor elementals, greater invisibility, or Otiluke's resilient sphere; two 5th level spell slots that could be used on cone of cold or contact other plane; and one 6th level spell slot that can be used on mass suggestion.
The new Spellcasting block for Zephyros now gives him either one or two uses of each spell, rather than presenting a list. This means Zephyros has his cantrips, two uses of gust of wind, two uses of levitate, two uses of magic missile, and one use each of cone of cold, contact other plane, greater invisibility, mass suggestion, nondetection, Otiluke’s resilient sphere, protection from energy, and tongues. This change to the Spellcasting block brings it in line with recent books and it will be the standard going forward in Dungeons & Dragons.