Reduced Threat. A reduced-threat monster takes a −2 penalty on attack rolls (included in the stat block), ability checks (included in the stat block for skill proficiencies), saving throws (included in the stat block for saving throw proficiencies), and saving throw DCs (included in the stat block).
Echolocation. The hook horror can't use its blindsight while deafened.
Keen Hearing. The hook horror has advantage on Wisdom (Perception) checks that rely on hearing.
Multiattack. The hook horror makes two hook attacks.
Hook. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit:11 (2d6 + 4) piercing damage.