Keen Hearing and Smell. The grimlock has advantage on Wisdom (Perception) checks that rely on hearing or smell.
Stone Camouflage. The grimlock has advantage on Dexterity (Stealth) checks made to hide in rocky terrain.
Spiked Bone Club. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d4 + 3) bludgeoning damage plus 2 (1d4) piercing damage.