#thirdtofifth monstrosity

Rat King
Small monstrosity, unaligned
Armor Class14
Hit Points 112 (15d6 + 60)
Speed30 ft., climb 15 ft., swim 15 ft.
Str12,Dex19,Con18,Int5,Wis14,Cha11
Condition Immunities charmed, frightened, paralyzed, petrified
Sensesdarkvision 60 ft. passive Perception 12
Languages-
Challenge5 (1800 XP)
Keen Smell. The rat king has advantage on Wisdom (Perception) checks that rely on smell.
Speak With Rats. The rat king can communicate with normal rats (including giant rats).
Actions
Multiattack. The rat king makes five bite attacks.
Bite.Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 6 (1d4+4) piercing damage. If the target is a creature, it must succeed on a DC 14 Constitution saving throw or contract a disease. Until the disease is cured, the target can’t regain hit points except by magical means, and the target’s hit point maximum decreases by 3 (1d6) every 24 hours. If the target’s hit point maximum drops to 0 as a result of this disease, the target dies.

Sometimes, several rats, endlessly writing in the darkness and muck, end up with their tails entangled and eventually knotted together. Sometimes, when this happens, the pain and torment of their restrained existence causes the rats’ sentience to merge into one single creature. Thoroughly infested with disease, the sight of a rat king can be enough to send an entire city into panic for the illnesses it may spread. A rat king is about 3 feet tall and weighs around 15 pounds. 

Originally from the Pathfinder Bestiary 4.

Abrian
Medium monstrosity, chaotic evil
Armor Class 15 (natural armor)
Hit Points 22 (4d8 + 4)
Speed50 ft.
Str13,Dex 16,Con 12, Int 7,Wis11,Cha10
Damage Resistancesthunder
Sensesdarkvision 60 ft. passive Perception 10
LanguagesAbyssal
Challenge1 (200 XP)
Actions
Multiattack. The abrian makes two attacks: one with its beak and one with its kick.
Beak.Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 6 (1d6+3) piercing damage.
Kick.Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit:7 (1d8+3) slashing damage.
Shriek (Recharge 5-6). The abrian lets out a horrible shriek. When it does, each creature that isn’t an abrian within 30 feet of the abrian must succeed on a DC 11 Constitution saving throw or be deafened for 1 hour. If the saving throw fails by 5 or more, the target is also stunned until the end of its next turn. A creature that succeeds on its save is immune to the Shriek of all abrians for 24 hours.

These ostrich-like birds lurk on the open plains of the Abyss, Gehenna, and other desolate regions of the outer planes. They are smarter than they look, and sometimes trade with nomads in those regions. They tend to travel in flocks of four to ten individuals, though a flock can have up to forty. In battle, they spread out and dart in and out of the fray in pairs, trying to outflank their opponents. They have black and orange feathers, and two small shrunken arms in place of wings, which are adequate for manipulating objects, but useless in combat. They stand around 6 feet tall and weigh around 250 lbs. 

Originally from the Fiend Folio. 

Yuan-Ti Ignan
Large monstrosity (yuan-ti), chaotic evil
Armor Class 15 (natural armor, shield)
Hit Points 104 (11d10 + 44)
Speed30 ft.
Str21,Dex13,Con18,Int6,Wis14,Cha11
SkillsDeception +3, Stealth +4
Damage Immunities fire
Damage Resistancespoison
Damage Vulnerabilities cold
Condition Immunitiespoisoned
Sensesdarkvision 120 ft. passive Perception 12
LanguagesAbyssal, Common, Draconic
Challenge7 (2900 XP)
Magic Resistance. The yuan-ti has advantage on saving throws against spells and other magical effects.
Magic Weapons. The yuan-ti’s weapon attacks are magical.
Actions
Multiattack. The yuan-ti makes four attacks: two with its mace, one with its gore, and one with its tail slap.
Mace.Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 12 (2d6+5) bludgeoning damage and 3 (1d6) fire damage.
Gore.Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 9 (1d8+5) piercing damage and 3 (1d6) fire damage.
Tail Slap. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 10 (1d10+5) bludgeoning damage and 3 (1d6) fire. If the target is a Large or smaller creature, it is grappled (escape DC 16). Until this grapple ends, the target is restrained, the yuan-ti can’t use its tail slap, and the target takes 15 (3d6+5) bludgeoning damage and 7 (2d6) fire damage at the start of each of the yuan-ti’s turns.

The result of crossbreeding between yuan-ti and salamanders, yuan-ti ignans are aggressive and brutal, with an affinity for fire. They are rarely enountered without greater yuan-ti as their masters, who consider them to be expendable. Fear of insurrection causes yuan-ti leadership to keep ignans apart from each other until they are ready to be fielded in battle. Some yuan-ti fortresses have fallen to ignan uprisings, and are occupied solely by the creatures. They tend to keep gems and coins as treasure; never flammable items. Yuan-ti ignans range between 10 and 14 feet long and weigh 250 to 400 lbs. The males tend to have red scales, while the females tend to have gray or brown scales. 

Originally from the Monster Manual IV.

Nightmare Beast
Huge monstrosity, chaotic evil
Armor Class 17 (natural armor)
Hit Points 202 (15d12 + 105)
Speed30 ft.
Str24,Dex13,Con25,Int8,Wis13,Cha11
Saving Throws Dex +6, Con +12
Damage Resistances bludgeoning, piercing, and slashing from nonmagical attacks
Condition Immunitiesfrightened
Sensesdarkvision 60 ft. passive Perception 11
LanguagesAbyssal
Challenge15 (13000 XP)
Augmented Critical. The nightmare beast’s weapon attacks score a critical hit on a roll of 19 or 20.
Magic Resistance. The nightmare beast has advantage on saving throws against spells and other magical effects.
Nightmares. Humanoids within 10 miles of the nightmare beast that need to sleep are plagued by constant nightmares and can’t gain the benefits of a long rest while they remain in the area.
Actions
Multiattack.The nightmare beast makes four attacks: one with its tusks, one with its bite, and two with its claws.
Bite.Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit:20 (3d8+7) piercing damage.
Tusks.Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit: 23 (3d10+7) piercing damage.
Claws.Melee Weapon Attack: +12 to hit, reach 10 ft., one target. Hit:17 (3d6+7) slashing damage.
Dread Trample. The nightmare beast moves up to its speed. During this movement, it can move through the spaces of Large or smaller creatures. A creature whose space the nightmare beast enters for the first time on a turn must make a DC 20 Dexterity saving throw, taking 44 (8d10) bludgeoning damage on a failed save, or half as much damage on a successful one. At the end of this movement, it may make one attack with its tusks.

The nightmare beast is a terrifying creature with tough dark gray hide with blue, purple, and brown spots splattered across it. Its beady red eyes glow in the dark. The nightmare beast lives in a cave deep in the wastes, picking the region clean of prey before hibernating for a year or more. After awakening, it is often so ravenous that its hunting spree drives all civilized life out of its territory. The nightmare beast does not collect treasure; the only treasure that is usually found in its lair is that which it has eaten in its rush to consume its prey. A nightmare beast stands around 20 feet tall. Its weight is unknown.

Originally from the Monster Manual II

Dunewinder
Huge monstrosity, unaligned
Armor Class 16 (natural armor)
Hit Points 178 (17d12 + 68)
Speed 50 ft., burrow 20 ft.
Str23,Dex15,Con19,Int5,Wis12,Cha11
Damage Immunitiesfire
Damage Resistances necrotic, poison
Damage Vulnerabilitiescold
Condition Immunities blinded, prone
Sensestremorsense 60 ft. passive Perception 11
Languages-
Challenge10 (5900 XP)
Death Throes. When the dunewinder dies, it explodes, and each creature within 60 feet of it must make a DC 16 Dexterity saving throw, taking 17 (5d6) piercing damage and 17 (5d6) poison damage on a failed save, or half as much damage on a successful one. 
Actions
Bite.Melee Weapon Attack: +8 to hit, reach 10 ft., one target.Hit: 22 (3d10+6) piercing damage. The target must make a DC 16 Constitution saving throw, taking 42 (12d6) poison damage on a failed save, or half as much damage on a successful one. The target is grappled (escape DC 18). Until this grapple ends, the target is restrained, and the dunewinder can’t use its bite on another target.
Fire Breath (Recharges After A Short Or Long Rest). The dunewinder exhales fire in a 60-foot line that is 10 feet wide. Each creature in that line must make a DC 16 Dexterity saving throw, taking 49 (14d6) fire damage on a failed save, or half as much damage on a successful one.

The desert cousins of the arctic remorhaz, dunewinders are named for their sidewinding motions as they travel through the sand. They prefer to weaken prey with a blast of their fire breath, before biting and strangling them to finish them off. Often, they lie in ambush just over the crest of a dune, waiting for prey to approach. These creatures are always encounters alone. Dunewinders can be up to 40 feet long.

Originally from Sandstorm

For a compilation of all of the monster stats so far posted here, visit this Pastebin link: https://pastebin.com/raw/YtEQ4LMA

Digester
Medium monstrosity, unaligned
Armor Class 14 (natural armor)
Hit Points 119 (14d8 + 56)
Speed60 ft.
Str17,Dex15,Con18,Int2,Wis12,Cha10
SkillsStealth +5
Damage Immunitiesacid
Sensesdarkvision 60 ft. passive Perception 11
Languages-
Challenge6 (2300 XP)
Keen Smell. The digester has advantage on Wisdom (Perception) checks that rely on smell.
Standing Leap. The digester’s long jump is up to 30 feet and its high jump is up to 15 feet, with or without a running start.
Actions
Multiattack.The digester makes two bite attacks.
Bite.Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 10 (2d6+3) piercing damage plus 10 (3d6) acid damage.
Acid Spray (Recharge 5-6). The digester sprays acid in a 30-foot cone. Each creature in that area must make a DC 14 Dexterity saving throw, taking 42 (12d6) acid damage on a failed save, or half as much damage on a successful one.

A digester is almost constantly hungry, though its insatiable appetite does not prevent it from being a cunning and patient hunter. It waits in ambush, springing on its foes and unleashing a spray of acid, and then biting and snapping until it acid glands refill. They are usually solitary, but packs of up to a half-dozen individuals have been recorded. They tend to live in tropical forests and hills, where its prey are most plentiful. A digester stands about 5 feet tall and is 7 feet long from snout to tail. It weighs about 350 pounds,

Originally from the Monster Manual.

Thrym Hound
Huge monstrosity, neutral evil
Armor Class 17 (natural armor)
Hit Points 175 (13d12 + 91)
Speed 40 ft.
Str24,Dex12,Con25,Int4,Wis18,Cha15
Damage Resistancescold
Senses passive Perception 14
Languages Common, Draconic, Giant
Challenge 10 (5900 XP)
Keen Smell. The Thrym hound has advantage on Wisdom (Perception) checks that rely on smell.
Ice-Spiked Hide. A creature that touches the Thrym hound or hits it with a melee attack while within 5 feet of it takes 2 (1d4) cold damage.
Actions
Multiattack.The Thrym hound makes one bite attack and two claw attacks.
Bite.Melee Weapon Attack: +11 to hit, reach 10 ft., one target.Hit: 17 (3d6+7) piercing damage plus 3 (1d6) cold damage.
Claw.Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit:14 (2d6+7) slashing damage plus 3 (1d6) cold damage.
Frigid Stare (Recharge 5-6). The Thrym hound’s eyes project bitter cold in a 60 foot line, 10 feet wide. Each creature in that area must make a DC 17 Dexterity saving throw, taking 45 (13d6) cold damage on a failed save, or half as much damage on a successful one. A creature that fails its save also has its speed halved until the end of its next turn.

These predators of the frozen waste are said to be a gift from the frost giant god  Thrym. Whether true or not, Thrym hounds are commonly kept as pets and warbeasts by the frost giants; though, they are also commonly encountered in the wild, sometimes alone, sometimes in packs. They sit comfortably at the top of the food chain, fearing only white dragons. Requiring only one large meal a year, these creatures often spend much of their time in the ice caves they make their lairs in. They do not keep treasure themselves, but it can often be found in their lairs among the bones of their victims. Thrym hounds stand around 12 feet tall, are around 30 feet long, and weigh approximately 15 tons.

Originally from the Monster Manual V.

Bearhound
Large monstrosity, neutral good
Armor Class 14 (natural armor)
Hit Points 133 (14d10 + 56)
Speed40 ft.
Str23,Dex15,Con18,Int16,Wis14,Cha12
Saving Throws Dex +5, Wis +5
SkillsStealth +5, Survival +5, Perception +5
Damage Resistances cold
Sensesdarkvision 60 ft., passive Perception 15
LanguagesCommon, Sylvan
Challenge7 (2900 XP)
Keen Smell. The bearhound has advantage on Wisdom (Perception) checks that rely on smell.
Magic Weapons. The bearhound’s weapon attacks are magical.
Trackless Step. The bearhound can’t be tracked except by magical means.
Hunter’s Savagery (3/Day). As a bonus action, the bearhound can add 1d10 to its next attack or damage roll with a melee weapon attack.
Actions
Multiattack. The bearhound makes three attacks: one with its bite, and two with its claws.
Bite.Melee Weapon Attack: +9 to hit, reach 5 ft., one target.Hit:15 (2d8+6) piercing damage. If the target is a Large or smaller creature, it must succeed on a DC 17 Strength saving throw or be knocked prone.
Claw.Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit:10 (1d8+6) slashing damage.

Bearhounds are elusive loners, such that they are considered a myth by many. They live alone, hunting and keeping to themselves, only rarely finding a cause worthy of their attention. In these cases, they make for powerful allies. These creatures stand 6-½ feet tall and weigh around 2000 pounds.

Originally from the Monster Manual III.

Braxat
Large monstrosity, neutral evil
Armor Class 17 (natural armor)
Hit Points 126 (12d10 + 60)
Speed30 ft.
Str23,Dex12,Con20,Int15,Wis12,Cha11
Saving Throws Dex +5, Con +9, Wis +5
Sensesdarkvision 60 ft. passive Perception 11
LanguagesGiant, telepathy 120 ft.
Challenge9 (5000 XP)
Innate Spellcasting.
The braxat’s spellcasting ability is Intelligence (spell save DC 14). The braxat can innately cast the following spells, requiring no material components:
At will: dimension door
1/day each: confusion, feeblemind
Actions
Multiattack. The braxat makes three attacks: two with its greatclub and one with its gore.
Greatclub.Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 15 (2d8+6) bludgeoning damage.
Gore.Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 13 (2d6+6) piercing damage.
Cone Of Cold (Recharge 5-6). The braxat exhales a blast of cold in a 30-foot cone. Each creature in that area must make a DC 17 Dexterity saving throw, taking 27 (6d8) cold damage on a failed save, or half as much damage on a successful one.
Mind Blast (Recharge 6). The braxat magically emits psychic energy in a 60-foot cone. Each creature in that area must succeed on a DC 14 Intelligence saving throw or take 22 (4d8 + 4) psychic damage and be stunned for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

These vicious creatures hunt in the mountains and deserts of the world, savoring the joy of stalking intelligent beings. Unless truly desperate, a braxat will not subsist on animals; instead, it seeks humanoid flesh and craves the taste of it. They raid humanoid settlements, alone or in small bands of up to six individuals. Despite their brutish appearance, they are quite cunning and difficult to trap. The truly formidable (or truly insane) will hunt braxats for sport, hoping to take one of their valuable horns as a trophy. Looking something like a cross between a rhinoceros and a lizard, a braxat stands around 15 feet tall. Most speak only the giant tongue, but a few learn Common as well. 

Originally from the Monster Manual II