Armor Class 19 (natural armor)
Hit Points 189 (18d10 + 90)
Speed 30 ft.
Saving Throws STR +8, CON +9
Skills Perception +2
Senses darkvision 60 ft., passive Perception 12
Languages —
Challenge 12
Multiattack. The gray render makes three attacks: one with its bite and two with its claws.
Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 17 (2d12 + 4) piercing damage. If the target is Medium or smaller, the target must succeed on a DC 16 Strength saving throw or be knocked prone.
Claws. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 13 (2d8 + 4) slashing damage. If the target is prone an additional 7 (2d6) bludgeoning damage is dealt to the target.
Bloody Rampage. When the gray render takes damage, it makes one attack with its claws against a random creature within its reach, other than its master.
Mordenkainen's Tome of Foes, p. 209