As noted elsewhere, Holmes follows Supplement I in giving monsters D8 for hit dice. They also use Greyhawk-style attacks with variable damage, despite the text's implying in places that such a complexity would be reserved to AD&D.
Holmes addresses the issue of balancing the power of monsters against the experience of the characters facing them in this way:
In setting up his dungeon, the Dungeon Master should be guided by the table given under Wandering Monsters, so that adventurers have a reasonable chance of survival. There is endless opportunity for inventiveness in the game, however, and if a high hit dice monster is desired, ways can be invented to scale it down so that a low level party can have a chance of defeating it. If one wanted to use a chimera, for instance, in a campaign with low level characters, the creature could be scaled down. Maybe it ran into a high level magic-user and was partially shrunk by a magic spell, reducing its high points. Or there might be a special magic sword, effective only against this chimera, hidden in the dungeon, and the adventurers given a hint or a legend that might lead them to it. In the interest of maintaining the balance of the game, however, a small or weak monster must not have a treasure anything like the hoard of a normal monster.Concerns about handing out too much and too little treasure, as well as the rate of experience gain have already been touched upon here.
Bandits get a lengthy entry, as in OD&D, breaking down the full composition of a force of these men, including armor, weapons, and magical accoutrements. Interestingly, Holmes continues to use OD&D's "supernormal characters" to refer to any character who has a class and levels. Basilisks are as in OD&D, as are berserkers, though I adore the fact that their entry ends with a two-word paragraph -- "No prisoners." (This seems to be a reference to the fact that many Men have captives/prisoners amongst them). Black puddings are as in OD&D, but there is no reference to gray puddings in Holmes. Blink dogs and bugbears follow Supplement I. Carrion crawlers and cockatrices are true to OD&D. Chimeras are slightly more potent in Holmes, as its goat horns do increased damage. The displacer beast follows Greyhawk and djinni get a much-lengthened entry, elucidating their magical powers in some detail. The doppelganger entry follows Supplement I, except that Holmes spells out exactly what the creature needs for certain saving throws, as opposed to simply saying that it saves as a 10th-level fighter.
Monsters continue tomorrow.