Each of the gorechimera's three heads has 76 (6d12 + 30) hit points and can be targeted individually to weaken it and hinder it's ability to use it's attacks. A head that has been decapitated or that has been killed by a critical hit cannot be revived by the gorechimera's heal ability.

If the dragon head is killed, the gorechimera cannot use its fire breath ability.

If the lion head is killed, the gorechimera cannot use its heal ability.

If the goat head is killed, the gorechimera cannot use its horns attack or its sleep ability.

The gorechimera's tail can be severed if it is dealt more than 30 slashing damage in a single turn. If it's tail has been severed, the gorechimera cannot use it's stinger attack. The severed tail regenerates after 3d10 days.

Multiattack.  The gorechimera can use its Frightful Presence. It then makes four attacks: one with its bite, one with its horns, one with its claws, and one with it's stinger. When its fire breath, heal, or sleep is available, it can use the it in place of its bite or horns.

Bite. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 15 (2d8 + 6) piercing damage.

Horns. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 20 (2d12 + 6) bludgeoning damage.

Claws. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

Stinger. Melee Weapon Attack: +11 to hit, reach 5 ft., one creature. Hit: 11 (1d8 + 6) piercing damage, and the target must make a DC 16 Constitution saving throw, taking 22 (4d10) poison damage on a failed save, or half as much damage on a successful one.

Frightful Presence. Each creature of the gorechimera's choice that is within 120 feet of the gorechimera and aware of it must succeed on a DC 16 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the gorechimera's Frightful Presence for the next 24 hours.

Fire Breath (Recharge 5–6). The dragon head exhales fire in a 15-foot cone. Each creature in that area must make a DC 18 Dexterity saving throw, taking 45 (13d6) fire damage on a failed save, or half as much damage on a successful one.

Heal (Recharge 5–6). The lion head's mane flares with a yellow light, healing the gorechimera for 35 (6d8 + 5) hit points. This healing can be divided up among the different heads and can revive a head reduced to below 0 hit points.

Sleep (Recharge 5–6). The goat's eyes glow purple and sends nearby creatures into a magical slumber. Each creature within a 30 foot sphere of the gorechimera must succeed on a DC 18 Constitution saving throw or fall unconscious for 10 minutes. This effect ends for a creature if the creature takes damage or someone uses an action to wake it.