Straight up conversion of this fella. I used the 5e Stone Golem as the base and threw in the Medusa-like petrification ability.
DOMINION FOSSIL GOLEM
Large construct, unaligned
Armour Class 17 (natural armour)
Hit Points 178 (17d10 + 85)
STR 22 (+6) DEX 9 (-1) CON 20 (+5)
INT 3 (-4) WIS 11 (+0) CHA 1 (-5)
Damage Immunities poison, psychic; bludgeoning, piercing, and slashing from non magical weapons that aren’t adamantine
Condition Immunities charmed, exhaustion, frightened, paralyzed, petrified, poisoned
Senses darkvision 120ft., passive Perception 10
Languages understands the languages of its creator but can’t speak
Challenge 10 (5,900 XP)
Immutable Form. The golem is immune to any spell or effect that would alter its form.
Magic Resistance. The golem has advantage on saving throws against spells and other magical effects.
Magic Weapons. The golem’s weapon attacks are magical.
Multiattack. The golem makes two petrifying slam attacks. When available it may also use a bonus action to use its slow gas attack.
Petrifying Slam. Melee Weapon Attack: +10 to hit, reach 5 ft., one target.
Hit: 19 (3d8 + 6) bludgeoning damage as well as suffer from a petrification attack. The creature must make a DC 17 Constitution saving throw. If the saving throw fails by 5 or more, the creature is instantly petrified. Otherwise, a creature that fails the save begins to turn to stone and is restrained . The restrained creature must repeat the saving throw at the end of its next turn, becoming petrified on a failure or ending the effect on a success. The petrification lasts until the creature is freed by the greater restoration spell or other magic. This specialized golem doesn’t petrify the brain allowing the Dominion to harvest the petrified creatures brain at a later date.
Slow (Recharge 5-6). The golem targets one or more creatures it can see within 10 feet of it. Each target must make a DC 17 Wisdom saving throw against this magic. On a failed save, a target can’t use reactions, its speed is halved, and it can’t make more than one attack on its turn. In addition, the target can take either an action or a bonus action on its turn, not both. These effects last for 1 minute. A target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
Fossilized bones make up the body of this animated construct. It seems to be the fossilized remains of a very big neh-thalgaa.