Merman: Mermen first appeared in OD&D Vol. 2, and were expanded upon in Supplement II: Blackmoor. Their Number Appearing has lessened from 30-300 to 20-200. Their speed on land has decreased from 3” to 1”, but their swimming speed has increased from 15” to 18”. Their Hit Dice has gone back to 1+1; in OD&D they had similar characteristics to berserkers (including the HD above), but in Supplement II they had been reduced to 1 Hit Dice. Supplement II had also given them a bite attack and two hand attacks; now they simply use their weapons.
Of course mermen are aquatic, but we learn that they favour the warm and tropical areas. It’s said that they sometimes leave the water to sun themselves, and this is interesting, because in Supplement II they take damage while out of water. The damage is higher in daylight, as well. Obviously this is no longer the case. Mermen dwellings are described for the first time, with most of them being a reef or cliff riddled with tunnels, and the rest being villages of shells and coral. We also learn that they have women and young, but that’s generally true for most of Gary’s monsters. Also, they speak their own language, and some speak locathah, implying either a friendship or an enmity with that race (almost certainly the latter).
Barracuda are introduced as common pets and guards for mermen, but something that has been taken away from them are seahorses. Supplement II describes them as riding seahorses, but I think it’s pretty clear in the Monster Manual that we’re dealing with the standard fish-tailed mermen that wouldn’t be able to mount anything.
In OD&D mermen used tridents, darts, slings and crossbows. Here they can have tridents, daggers, crossbows, javelins and nets. The slings are gone, because they make no damn sense as an aquatic weapon. Many are also armed with hooks for grappling ships, just as they were in Supplement II. The rules for that are pretty much the same.
With the great number of differences between the mermen of AD&D and those from Supplement II, I think that I’m going to have to declare that there are two different species. The ones from Supplement II live in and around the Blackmoor area, and have legs. The others from OD&D and AD&D live further south, and have fish-tails. Sorted.
Mimic: The mimic is making its first appearance here. It’s not really certain what a mimic’s true form is, but they can disguise themselves as anything made out of stone or wood. As soon as someone touches one, it secretes a glue to hold him fast then slams him with a pseudopod.
I was interested to discover that there are two varieties of mimic. Regular mimics have less Hit Dice, but are smarter, and will probably be friendly if offered food. Then there are the “killer mimics”, which are bigger, meaner, and only semi-intelligent. I’ve only ever seen mimics portrayed in the latter fashion, but the more potentially whimsical nature of the former strikes my fancy. They even have their own language. I’m wondering about the distinction between the two. Are they different types of the same race, or is it perhaps a natural part of the mimic aging process to go insane?
Mind Flayer: Mind flayers made their debut in Supplement I: Greyhawk, and were greatly expanded with the addition of psionics in Supplement III: Eldritch Wizardry. Gary must have been super-happy with the stats for these guys, because all he’s changed is the addition of a single hit point. About the only other thing that has been changed is that their mind blast is now a cone instead of having a blast radius. The DM doesn’t get to pick their psionic abilities now: they all get levitation, domination, ESP, body equilibrium, astral projection and probability travel. Otherwise you’re looking at basically the same monster, with the small addition that there are now rumours going around of a mind flayer city beneath the earth.