Colosso Assassino

Charge. If the Colossus moves at least 15 feet straight toward a target and then hits it with a gore attack on the same turn, the target takes an extra 11 (2d10) piercing damage. If the target is a creature, it must succeed on a DC 16 Strength saving throw or will fall prone behind the Colossus.

Fear Aura. Any creature within 20 feet of the Colossus when he appears must make a DC 15 Wisdom saving throw, on a failed save, the creature is frightened until the start of its next turn. If a creature's saving throw is successful, the creature is immune to the Colossu's Fear Aura for the next 24 hours.

Shapechanger. The Colossus can use its bonus action to polymorph into a Medium shape of itself or back into its true form. Its statistics are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.

Multiattack. The Colossus makes three melee attacaks: two Claws attacks and one Bite attack.

Claw. Melee Weapon Attack: +8 to hit, reach 10 ft. , one target. Hit: 9 (1d8 + 5) bludgeoning damage, and the target is grappled (escape DC 16). The Colossus can grapple only one target. 

Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target grappled. Hit: 27 (4d10 + 5) piercing damage. If the target is a creature, it must succeed on a DC 14 Constitution saving throw or take 2 (1d4) piercing damage at the start of each of its turns due to a fiendish wound. Each time the Colossus hits the wounded target with this attack, the damage dealt by the wound increases by 2 (1d4), up to a maximum of 5d4. Any creature can take an action to stanch the wound with a successful DC 13 Wisdom (Medicine) check. The wound also closes if the target receives magical healing.

Gore. Melee Weapon Attack: +8 to hit, reach 10ft., one target. Hit: 43 (7d10 + 5) piercing damage.