I’m treating the catoblepas and MM gorgon as variations on the same thing, so don’t get confused later. The catoblepas has received a few variations in 3pp because the monster is public domain but was never included in the SRD. I’m gonna simplify all that into a series of random generation tables.
Melee attack, roll 1d4
1. Gore attack, roll to determine damage
2. Tail strike, roll to determine damage
3. Mane of snakes, deal special attack damage
4. Long neck doubles melee reach, roll 1d3 to determine attack from the above list
Gore attack damage, roll 1d3
1. Curling horns, bludgeoning damage
2. Pointed, antlers and/or tusks, piercing damage
3. Mix, bludgeoning & piercing damage
Tail damage, roll 1d4
1. Mace tail, bludgeoning damage
2. Spiked tail, piercing damage
3. Spiked mace tail, bludgeoning & piercing damage
4. Long tail doubles melee reach, roll 1d3 to determine attack from the above list
Defenses, roll 1d4
1. Thick hairy hide and/or bony plates, no additional effect
2. Metallic scales, adds vulnerability to electricity/lightning damage
3. Horrible stench, opponents must hold breath to avoid taking psychic/poison damage
4. Defensive spines, deal piercing damage if an opponent successfully hits in melee
Special attack, roll 1d3
1. Gaze attack*
2. Breath weapon
3. Eye ray attack*
(Roll on following table to determine damage)
*Cannot be used if the catoblepas’ eyes are covered or damaged. This include the eyes provided by the mane of serpents.
Special attack damage, roll 1d6
1. Poison damage, and resistant to poison damage; has violet pigmentation
2. Necrotic damage, and immune to necrotic damage but vulnerable to radiant damage; has black pigmentation
3. Acid damage, and resistant to acid damage; has green pigmentation
4. Petrifaction, and immune to petrifaction; has gray/silvery pigmentation
5. Fire damage, and immune to fire damage but vulnerable to cold damage; has red/orange/yellow pigmentation
6. Cold damage, and immune to cold damage but vulnerable to fire damage; has blue/white pigmentation
Throw spikes attack, roll 1d4
(If the catoblepas has spikes/spines from its tail or defense then roll this table, otherwise ignore)
1. No additional effect
2. Can throw spikes as a ranged attack, like manticore
3. Spines deal special attack damage
4. Spines can be thrown & deal special attack damage
Spit venom attack, role 1d2
(If the catoblepas has a mane of serpents then roll this table, otherwise ignore)
1. No additional effect
2. The snakes can spit venom as a ranged attack, dealing special attack damage
If desired, roll multiple times on single tables, ignoring nonsensical results.