Multiattack. The Catoblepas makes two attacks, using Tai or Gore in any combination.
Tail. Melee Attack Roll: +7 to hit, reach 10 ft. Hit: 21 (5d6 + 4) bludgeoning damage, and the target must succeed on a DC 16 Constitution saving throw or be stunned until the start of the catoblepas’s next turn.
Gore. Melee Attack Roll: +7 to hit. Hit: 22 (2d10 + 6) piercing damage, target is thrown 10 ft. and is prone.
Death Ray (Recharge 4-6). Catoblepas can replace its Multiattack with Death Ray. Targets one creature within 30 feet of it. The target must make a DC 16 Constitution saving throw, taking 36 (8d8) necrotic damage on a failed save, or half as much damage on a successful one. If the saving throw fails by 5 or more, the target instead takes 64 necrotic damage. The target dies if reduced to 0 hit points by this ray.
Stench. Any creature other than a catoblepas that starts its turn within 10 feet of the catoblepas must succeed on a DC 16 Constitution saving throw or be poisoned until the start of the creature’s next turn. On a successful saving throw, the creature is immune to the Stench of any catoblepas for 1 hour.