Thoughts on Volo's Guide to Monsters
by Kilr KowalskiChapter 1 Monster lore
Beholder stuff- although they are sometimes regarded as canon, they are not as Mystaran as other monsters: not so useful
Most of the giant stuff is pretty good from wha I can tell.
The gnoll fluff suffers from an emphasis on being some form of demonic avatars of hunger ( i think this comes from some 4th ed fluff), although they still worship Yeenoghu (established in 1st or 2nd Ed to be the same as Yagrai). Alot of the "mind of a gnoll" stuff is not consistent with Mystara gnoll canon. e.g peaceful tribes near Cimmaron county and organised tribes in the Gnollheim hills. If you liked Flinds being lawful non-gnolls that the gnolls seemed to think were ace that has gone but they weren't clearly mystara canon AFAIK. So: gnolls a bit of a wash i think.
The goblinoids fluff seems pretty in line with the Mystaran multicultural goblinoid tribes, although with different deities (or at least names, Maglubiyet has always fit well with Wogar and Hruggek fits with Bartziluth. Even Khurgorbaeyag fits with Leptar.)
Hags' stuff sounds pretty useful for fluff
The Kobold stuff suffers from the later edition change of kobolds into a draconic offshoot, but ignoring most of the dragon related fluff (including that they are cold blooded and lay eggs!) most of the fluff is pretty good. I don't dig Urds, or different "scale colours" etc but again, this is easily ignored.
Mind flayers- not so useful I would think
The Orc section Fluff - "Life in the tribe" onwards is pretty good until it starts talking about the FR gods again, right up until the "Orc lairs" section which is again quite god-dy. The orc flaws and traits are good.
Yuan Ti- mostly irrelevant on Brun I would think.
Chapter 2 Character races:
Aasimir/Firbolg/Goliath - not so useful
Kenku- not so useful
Lizardfolk- I quite like their take and most of the fluff here.
Tabaxi- I guess they're fine for a cardboard cutout Rakasta like race.
Tritons are there and they are what you expect except that there is a bit of fluff saying that they originated on the elemental plane of water: take it or leave it. The nice bit is the fluff where they are automatic outsiders re: the surface world and they have a quirk mechanic which keys Players into remember that they are "strangers in a strange land"
The Bugbear, Goblin hobgoblin kobold and Orc 5th ed crunch for PCs is there of course which would be good for brokenlands/Yazak steppes folk and Orc's head peninsula folks.
Chapter 3 bestiary
Mostly not Mystara specific
by Håvard
Regarding the Goliaths, people here on The Piazza kind of sold me on the fact that they are the equivalent of Stalwarts from AC9, but I don't know how widely accepted that is. In any case I don't know how many people actually ever used Stalwarts?
Regarding the monster section, I think I saw the Catoblepas in there? I think they are supposed to be the same as the Necrozon from the Master Set, though the illustration in the Master Set make them look so much cooler than any other version I have seen.