The S Chapter is super long at 23 pages. Its also got a couple big entries in it.
Sahuagin
The Sahuagin are sort of the red headed step child of DND. Frank seems to love them judging by his posts and Tome, and I agree they are pretty cool (and easily the best underwater humanoid race). That said, they never get an appearance in anything mainstream as anything but a joke. 5e continues that tradition. Their new look for 5e is that of a green leech man. More octopus than anything else. It really does a good job of making you immediatley not care. I've always seen them as having skin like a shark and big shark grin mouths. In this they have the same fish head thing as the Kua-Toan. They are just really disappointing. The first pic also looks like his right shoulder is dislocated, but the 4 armed one is an alright drawing of a stupid concept. Sahuagin dwell in the deepest trenches of the ocean and raid the shores. That doesn't really seem to make logistical sense, but alright. In reading the older entries, apparently they used to dwell on the shallows. that makes a lot more sense. The next bit is about how they view themselves as the rulers of the oceans. A brief wikipedia reading on their history along with a glance through my 3.5 MM shows no sign of that in prior editions leading me back to my theory that someone in the 5e design process read the tomes. Now instead of having an ordered society that raises sharks as war dogs they worship a shark god, Sekolah who is given no motivations or description other than the idea that only female Sahuagin can be priestesses. Then its got a bunch on how they hate elves, and honestly thats a reoccuring theme in this book. I'm starting to think the 5e elves are just assholes. Statwise the CR1/2 Sahuagin can compete on land, and will own you under water. It can come on land for 4 hours, or just long enough to raid. Otherwise its a standard brute, who can also throw a spear. It should probably buy some armor though, as its AC is only 12. A Sahuagin priestess is a CR 2 foe with the same powers, but some cleric spells. They aren't a bad choice, but have a really low DC (12). Bless, hold person, spiritual weapon, mass healing word, etc. Lastly, we have stats for the Sahuagin Baron. Not sure why we don't get a king or leader, or something, but random court noble works too. He is the same stats as the main one, only with bigger numbers and CR 5. They make a big deal about how there are 4 armed mutants, but those don't get stats. Thats upsetting because the rest are all just the stock sahuagin with bigger numbers or spells. I'd like to see how the 4 armed dude fights. Even one of their shitty variants in a sidebar saying "Some have 4 arms, it gets twice as many attacks and is CR 1" or something.
This would be cool
Salamanders
Salamanders are a classical fantasy foe. 5e does a really bad job defining them. When they hatch from eggs they are a big snake, and then once they are a year old, they grow arms and jump 4 CR. The implication is that the CR 1 foe is straight up a baby. The rest of the book discusses the society of the salamanders, but nothing is said about the fire snakes again. Apparently just sometimes you find their babies, and you've got to kill them. Big bits on them also being slaves of the efreet after the azers rebelled. For some reason the salamanders hate the Azers for breaking free and not the efreeti for being slave holders. In addition to being efreeti slaves, they also have their own strict society with nobles and shit. The irony being that I can't see the efreeti respecting that and not asking His Holiness the Great King Fire Snake not to come hose off the orgy pillar or anything. So sure they have an elaborate society. I just don't see it ever coming into play. The fire snake has the exact properties you'd expect. If you hit it you take fire damage, and if it hits you same deal. The actual salamander looks pretty sweet and has some wicked moustaches. He has 2. He has the same powers, but has a free grappling tail.
Satyr
Satyrs have a great tradition in fantasy of being horny drunks. 5e continues this and expands on it. Its all the classical stuff, and their description then goes into how they will "Sneak through a well-defended garden to gaze upon a beautiful lad or lass". So now ontop of being world class hedonists, they also jerk it in the bushes outside your window. Fun monster mearls. He also spells out that they give no consequences of the hedonism they incite in others. Just in case you'd think "wait maybe they have some self control and realize that jerking it in the bushes isn't social acceptable". Stat wise, they are just a shitty fighter who randomly has magic resistance and is CR 1/2. So when he pulls this shit on your PC (because you know the DM will), you can just kill it and be done. These hilareous rape beasts are also CN aligned, because why not. Its the "I don't mean to be racist but..." excuse. I don't have evil intents, I just really need to watch you shower that makes me a decent dude right? Its got as much text devoted to telling the DM how to fuck you with these as it does to a variant. The variant gives him his satyr pipes, which you'd think would be iconic to the monster. You'd think wrong. These give it the ability to charm, scare, or put people to sleep. In case you didn't get that they were rapists. THis doesn't increase the CR for some reason. It doesn't mention what happens if you steal the pipes, but presumably they don't work because Fuck You. This is probably the worst monster in the book, because its just one long "And then your animal companion rapes you" joke. This is one of the first that makes me mad out of "Fuck you" and less out of "This is the worst thing ever".
Scarecrow
Apparently this was popular enough to keep being reprinted. Its just another animated object, but this one is CE and has a terrifying glare power. Its got the Fuck You hide power, but it only looks like a normal scarecrow. So if you know about them, you light it on fire anyway. Basically it works once. Its terrifying glare power forces 1 person to make a DC 11 wis save and be frightened and paralyzed until its next turn. They are CR 1, but I can't see how it would be a challenge for anyone. Also, no info on how to make them. Also, the art makes it very clear that this is the scarecrow from batman, but only the most modern looks for him.
This one. He even has the finger claw spikes
Shadow
Another ghost, this one is opne created by a shadow killing another someone and spawning one. No insight into how the first one was made, but thats kind of OK. They are CR 1/2, but have so many immunities and resistances you actually have a hard time unless you have a cleric. No flight speed seems weird. Its melee attack actually drains your strength which is suprising for 5e. If that str drain kills you and you are non-evil a new shadow arises 1d4 hours later. This is pretty solid overall. Ill make it #9 in ones I don't hate. The pic is cool too. My only real gripe is that it doesn't fly for some reason.
Shambling Mound
Another classic, this is always welcome and always problematic. The fluff on this spends a good time making them seem creepy, destructive on purpose, and "Ever-hungry Horrors" and so of course the book says they are unaligned. Its fluff also mentions the ability to feign death and regenerate quickly, but the stats don't. So unless your DM read all the fluff you only have to fight it once. Otherwise its a pretty solid CR 5. Lots of HP, but slow speed means you can probably just kite it. Being a swamp monster means that might actually be hard. It can engulf people for damage that at this level is decent.
Shield Guardian
This is yet another set of animated armor. Because we needed more. Basically these are created by mages, who use them as an extra HP pool. They wear an amulet and the construct takes half their damage. Its actually new for the "animated armor" monster in this book. Crafting them takes 1 week and 1000gp which was shocking information to find in this book. It makes no mention of who can craft one, if you have to be a wizard, or what the materials are but shit this is a start. I'd also ask that every PC i played with 1000gp to start just arbitrarily start with one. The fluff is lame and mostly an explanation of how the amulet works, but the bit about transfering ownership to whoever physically holds the amulet is cool. Their example is even killing a dude and stealing his amulet. Exactly what the PCs actually want to know.
Skeleton
Also not a template. Instead we get stats for 3 types of skeleton, and I guess you are supposed to match what you want to one of these 3 things? By their prior definitions of unaligned and constructs you'd think that things animated to do a task would be unaligned. But because they were animated by evil dudes with evil magic to do an evil task, they are LE. This is sort of a traditional problem with but a new edition is the time to fix it. The bits on habitual behaviors are nice. Apparently if left alone they pantomime actions from their past life. That really drives home the Unaligned alignment to me, but somehow they landed on CE. I think just out of tradition. The stats are for Skeleton (medium sized and CR 1/4), Minotaur Skeleton (Large sized with charge powers and CR 2), and Warhorse Skeleton (Large sized and CR 1/2). If you want a skeletal anything else, fuck you. No skeletal birds or wolves, or dragons, or giants, or sharks, anything. They don't spend a lot of effort on skeletons and there isn't a lot more to discuss. Just mostly, Fuck You.
Slaadi
Slaad are always fun. Unless 5e wrote them. Its full of fun as 5e explains the chaotic alignment. You get things like this "Slaadi are undisciplined and have no formal hierarchy, although weaker slaadi obey stronger ones". That sounds like a hierarchy to me. Here they bring Primus back and explain that long ago he made some prisim with the power of low. He threw it into limbo thinking that would do something. It got corrupted by chaos and became the Spawning Stone which started to make Slaadi for no reason. Its got a bit on birth and reproduction and they still implant with eggs which is sweet. You've also still got to learn the awkward Red slaadi spawn blue and green slaad cycle thing which is still annoying. Each color slaad gets a paragraph talking about how they spawn, but the only one of note is Death Slaad, which echos the themes of Chaos is another flavor of Evil. These are suffused with negative energy and "exemplify evils corruption of chaos" which I think means it shows how evil has co-opted chaos to mean the same thing. I don't really know though, thats the sort of half concepts that make L vs C hard to discuss in DND. It throws a variant on this page giving them a magic control gem, that sits in their brain. If you get it, they have to obey you which seems like a Lawful trait to me. If you can bind one and incapacitate it, you can make a DC 20 medicine check. I had to check and apparently medicine is the new name for the heal skill FYI. Failure does 22 damage, but other than that go at it until success. Meaning, you can probably succeed eventually without training. The weakest one has 93 hit points. Its very believable that your PCs could have some slaad paling around with them, but I'd expect your DM not to mention this variant rule, or not to play with it. Next page is pics of red/blue/green and gray slaadi. They are all really well drawn but the green one looks dumb. Its got a frog on his shoulder and a staff making it look like he is sane enough to sit and do stuff. the third slaad page gives us a B&W picture of a tadpole bursting from a dudes chest. This is important because it reminds DMs thats a thing, and I've had plenty forget about it until I bring it up mid fight. All Slaadi are dumb melee dudes with regeneration (makes it easier to extract that gem) a bunch of arbitrart resistances and a magic resistance. The slaad get 5 pages, which is a lot for 5e, so I'm going kind of quick really, but stat wise they are all basically the same. Of note, Green get some spells, but shitty ones. They can shapechange at will to medium or small creatures, cast 2 fears, 2 invis, and 1 fireball. This is probably the best one in the list honestly, as its spells give it some different ability. Also it can hurl flame 60ft. The Gray Slaad has the same shapechange at will power, and has 1/day planeshift, and then 2/day fear, fly, fireball, tongues. Basically once its done its spells its done, and since they are /day its relatively lame. Also its got a greatsword. This is super disappointing as I'd want them to be so insane they can't think of using a weapon or training in a martial one. The Death slaad gets his own page, and his art is probably the coolest. He also has the same spells + cloudkill. He also has a greatsword, and is also disappointing.
Specter
Another ghost. This one wins points for being the second ghost to start with S. Its a humanoid that was prevented from entering the afterlife, but not a zombie or ghost or anything else covered already. Really the fluff is just "Ghost". Its CR 1, which is lower than a ghost, but how ghostly can it be if its less than CR 4? Lets find out. Its incorporeal and flies, and has a whole host of immunities. Basically the only way to hurt it is to hit it with magic weapons, but you are level 1. So fuck you. its attack does damage and reduces your maximum if you fail a DC 10 con check. YOu probably have a bonus to con so you shouldn't fail this. They throw a half page entry in here for a variant. The variant has its own monster name "Poltergeist" and its CR 2. Its changes are that its invisible, with no action and it has a telekinetic thrust power. THis lets it throw shit at shit. These, by virtue of being flying, invis, and having a ranged attack, will probably TPK at CR 2. I love that someone saw how similar these two monsters are and made them variants, but we still got 15 different types of ghosts in this book. Like somehow someone broached the idea of consolidating like monsters to make room for other ones, and Mearls said yes. Then once he saw what that actually entailed (writing more stuff) he shut it down. So you got some consolidation, but not much. I hear occasionally that I'm too harsh on him directly for this book, but as the king of 5e, he is ultimately responsible. If someone does something stupid either he gave his blessing, or he let someone who gives bad blessings, give their blessing.
Sphinxes
You'd think there was one type of thing. The sphinx. But this is DND and someone once wrote up 500 variants on everything, and so someone consolidated "The core types of sphinx" into this entry instead of just giving stats for a sphinx and saying there aren't variants. Basically their fluff is the same as nagas except they guard stuff for gods, not some long lost race. Other than that its basically "They sit in a dungeon and guard a thing for gods, and ask riddles to see if you are worthy of getting the thing the guard." They give 2 types in 5e. Androsphinx's and Gynosphinx's. One is a dude on a lion and the other is a woman on a (Unspecified, but the pic looks like a lion). Other than that there isn't a lot of difference. Aside from some vague "The dude is about being gruff and valorous and courage" and "the lady is about looking deep in her eyes, and seeing how hot she is". Its the kind of sexist stupid shit that comes along with making a male and female version of a race different races. Reading either entry, you get no insight that they have wings. So when you look at the pic afterwards its a surprise. Sphinx's also have lairs, which kind of makes sense. We haven't seen a monster with a lair in a while, and I wonder if they were simply forgotten about. Its lair forces init rerolls, ages and deages (but never younger than 1, so you don't die, you just can't be a PC), moves time froward or backwards years, or it can planeshift the entire lair. Basically, its an excuse to introduce time travel into your game. This generally is a sign that you actually just want to end your game though, so who knows. Maybe Mearls has never played in a game where the DM had you go back in time and watched it just fall apart. Its not impossible, just super super hard. Stat wise, the dude has an int of 16 and the girl an int of 18. So you could very well be smarter than them, especially considering its a CR 17 (dude) or 11 (Girl) foe. The dude has spells which is nice, unfortunatly they are for healbots. So its not particularly effective. Its only 6th level spell is heroes feast. WTF is that? Its got roar powers that are kind of cool, blasting everyone in 500ft and forcing wisdom or con saves DC 18. So some people are probably affected. The girl has less spells but they are also shitty in the same vein. She also can't roar. At least these arent Good aligned out of some sort of "Godliness is goodness" thing.
Sprite
The sprite art is cool, in that its a dude sprite. You don't see that often.Then you read and you realize these are dude pixies and you hit the same problems I just described for sphinxes. All pixies are girls and they hate violence and love giggling. All sprites are boys and they are warriors. You can make the assumption that they are the same race because the entire sprite description is erither the same as pixies, or a contrast with pixies. (Unlike pixies...) Stat wise these are CR 1/4, but can go invisable. They also have poisoned arrows. So basically what I described about how to make pixies a TPK? These guys do. Also they have 2 HP, not 1. Because boys are tough. For those asking about saves that arent con/wis they have a Charisma 10 save power that lets them learn your "Current emotional state" on a pass and they get your alignment too if you fail.
Stirge
Stirges don't get a whole page. They are on a half page with the next monster. It makes their entry seem cramped. It gives no insight into where they are found, where they came from or anything other than "These are mosquito but bigger and grosser". Its CR 1/8 and has a blood drain power. If it hits it auto grapples and you take damage. Once attached you can spend your action to unattach them. Apparently it also unattaches after it does 20 damage and then it presumably latches onto someone else. This seems like a bad tactic.
Succubus/Incubus
These are split between 1.5 pages. The half page shared with a stirge is fluff, about how they live on the lower planes and are not demons or devils anymore. Now they simply serve devils, demons, night hags, rakshasas and yugoloyhs. Interesting bit of info. Any succusbus and become an incubus and vice versa. So enjoy that surprise with your succubus harems. It makes a big point that they don't actually sleep with people anymore though. Instead they sneak into your room and watch you sleep and give you dreams about your desires. The picture is just a hot goth chick in lingerie with bat wings, but its also got an incubus. She looks like some sort of potential dominatrix, but he looks like he is the submissive in the relationship. Thats cool and all, but not really what I've gathered incubuses are about. Stat wise they are CR 4, but you shouldn't fight them. They will die immediatly in a combat, but can charm people for a day DC 15 wisdom save or die. This means it might snag your fighter or whoever does lots of damage. Then the fight is a lot harder. Although if you hit the target they get another save. If it has you charmed, it can kiss you forcing Con saves that could be lethal and it seriously drains your max HP. But it seems worthless if it only works on someone who is charmed.