The "shark of the prairies," the terrifying Jawjack seems to have been built entirely for two activities: running and eating.
When simply standing and watching for prey (which they can easily do from their height; a good half again higher than a horse), a jawjack looks a bit like a muscular kangaroo with a long, forked tail: all muscle and hardened hide, with a blunt head, large nostrils (making it highly perceptive of its environment), and prominent incisors. It appears to have no arms, just its two back legs, at least until it opens its mouth.
When it pursues and nears prey, a jawjack's mandibles expand into appendages that would be effective arms on other creatures, creating a massive, fang-rimmed mouth that can consume a large dog whole. Legendary explorer Tarn Farstrider observed a jawjack swallow one half of a zebra and just stand there, noisily sucking on the unfortunate animal like a popsicle.
It can also use its mandibles to snare and scoop smaller, agile prey like rabbits into its mouth, making it a formidable hunter. They also hunt in packs of 2 to 8, squealing to each other like pigs to communicate danger. These infamous sounds are known to local tribes of sapients as "the screams of death" and greatly feared.
This is a big, tough creature, so I searched for CR 7 to 10 creatures of size "large." I wanted something simple, too -- these creatures would not be slinging spells or using complex strategies. I settled on the howler, a fiend with pack tactics, two bite attacks, and a mind-rending howl. I'll swap that out for the Scream of Death. I'll also remove a few of the howler's damage resistances and condition immunity, as well as its darkvision, in favor of a 20-foot climb speed, 10 more HP, and a 10-foot reach on its bite attacks.
OK, I think we're ready to go!
Homebrewery stat block:
Large creature, unaligned
- Armor Class 16
- Hit Points 100 (12d10 + 34)
- Speed 40 ft., climb 20 ft.
STR DEX CON INT WIS CHA 17 (+3) 16 (+3) 15 (+2) 5 (-3) 20 (+5) 6 (-2)
- Skills Perception +8
- Damage Resistances bludgeoning, piercing, and slashing from non-magical attacks
- Senses Passive Perception 15
- Languages --
- Challenge 8 (3,900 XP)
Pack Tactics. A jawjack has advantage on attack rolls against a creature if at least one of the jawjack's allies is within 5 feet of the creature and the ally isn't incapacitated.
Multiattack. The jawjack makes two bite attacks.
Bite. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit 10 (2d6 + 3) slashing damage, plus 22 (4d10) slashing damage if the target is frightened. This attack ignores damage resistance.
Scream of Death. The jawjack emites a squeal in a 60-foot cone. Each creature in that area that isn't deafened must succeed on a DC 16 Wisdom saving throw or be frightened until the end of the jawjack's next turn. While a creature is frightened in this way, its speed is halved, and it is incapacitated. A target that successfully saves is immune to the Scream of Death of all jawjacks for the next 24 hours.