Gorgons: Gorgons, which first appeared in OD&D Vol. 2, are still metal-skinned bulls with a petrifying breath weapon, and that makes them among my all-time favourite monsters. They haven’t changed at all statistically, although their breath weapon now has a more well-defined area of effect, and a limit on the number of times it can be used in a day. The entry here is actually quite sparse, as though Gary realised that a metal-skinned bull was already rad enough. We don’t need any ecology nonsense detracting from it’s majestic awesomeness.
Gray Ooze: Gray Ooze also made its first appearance in OD&D Vol. 2. They now have a value for Number Appearing, whereas before this was blank. Thier Hit Dice has increased slightly from 3 to 3+3. Their immunities haven’t changed much, except that they are now specifically immune to all spells except those that use lightning. They are still subject to damage from normal weapons, but those weapons are now said to possibly corrode or break. They are also said to strike like snakes when attacking, which was not detailed before. I’m also really happy to see that they’ve retained their latent psychic abilities from Supplement III, and can hit anyone who uses psionics near them with a psychic crush. There’s something about psionically-powered slimes that really resonates with me.
Green Slime: There are no changes to the basics of green slime, although their relative deadliness to OD&D can depend on your interpretation of the rules. In AD&D, it takes a slime 1-4 melee rounds to turn any creature it contacts into green slime (no resurrection possible!). In OD&D, it took one turn, but the use of word turn was ambiguous in those rules. It could mean ten combat rounds, or it could mean a single round, and there’s a world of difference between the two. As usual, I will probably interpret the rules to be the most fair to the players, but it's a moot point once we get to AD&D anyway. Oh, and green slimes are specifically said to be able to sense vibrations and drop on people passing underneath, so thay are at least a little more of a threat now.
Griffon: The only change to griffons is that their Number Appearing has decreased from 2-16 to 2-12. There are also some extra details about whether their young will be present in a nest, because Gary has thrown in the option of taking them and selling them for thousands of gold pieces.
Groaning Spirit: The only mention of a Groaning Spirit in previous D&D books was in Supplement III, under the description for the Iron Flask of Tuerny the Merciless. But that reference to a demon or devil of small power has no connection to this new monster, more commonly known as the Banshee. As far as undead go they have an unusually specific origin, being the spirits of evil female elves, something we’re assured is very rare. (Although, come to think of it, that describes pretty much the entirety of dark elf civilisation. Does every female drow become a banshee after death?) They have the usual raft of undead immunities, and can’t be harmed by non-magical weapons. Their main attack is a wail that kills everything within 30 feet that doesn’t make its saving throw. An exorcise spell will kill one outright, but just for fun I’m going to check the range on that – and as I suspected, it is 10 feet, so your cleric will have to get well within that banshee’s wail to get this spell off.