Graphorns are an interesting challenge because while they are more than capable of defending themselves they’re also an endangered species. I designed them to be tough by themselves, but in a pack they are absolutely lethal. Given that they’re mountain dwellers I gave them a few abilities that favor combat tactics employing mountainous terrain. I also took the fact that they’re hides are tougher than a dragon’s I gave them a high armor class and a decent hp pool. There are accounts of these beasts being used as mounts by trolls so if you want to employ that tactic go for it.
Huge beast, neutral
Armor Class 22 (natural armor)
Hit Points 236
Speed 75 ft., climb 50 ft.
Str 20 Dex 18 Con 20 Int 8 Wis 10 Cha 10
Saving Throws Str +8, Con +9
Damage Resistances bludgeoning, piercing, and slashing from non-magical weapons.
Skills Athletics +8, Intimidation+5, Perception +5
Condition Immunities frightened, stunned
Senses low-light vision 50 ft., passive Perception 10
Challenge 16 (15,000 XP)
Keen Hearing and Smell. The graphorn has advantage on Wisdom (Perception) checks made that rely on hearing or smell.
Magical Resistance. The graphorn has resistance advantage on saving throws against spells and other magical effects.
Pack Tactics. The graphorn has advantage on an attack roll against a creature if at least one of the graphorn’s allies is within 5 ft. of the creature and the ally isn’t incapacitated.
Rock Walk. The graphorn can move across and climb rock surfaces without need to make an ability check. Additionally, any difficult terrain composed of rocks or boulders doesn’t cost it extra movement.
Multiattack. The graphorn uses gore and makes 2 attacks with strike and one whipping tail against up to 3 targets.
Gore. Melee Weapon Attack. +6 to hit, reach 5 ft., one target. Hit: target takes 14 (1d10+6) piercing damage. Target must also make a DC 16 Dexterity saving throw, on a failed save the target is knocked prone.
Strike. Melee Weapon Attack. +6 to hit, reach 5 ft., one target. Hit: Target takes 12 (1d10+4) piercing damage. If the graphorn only uses one strike this turn the target is grappled.
Whipping Tail. Melee Weapon Attack. +3 to hit, reach 15 ft., one target. Hit: Target takes 10 (1d8+3) slashing damage and the target is knocked prone.