Colossus Slayer. Once during its turn when the allosaurus hits a creature with an attack, the creature takes an extra 1d8 damage if it's below its hit point maximum. Pack Tactics. The allosaurus has advantage on an attack roll against a creature if at least one of the allosaurus's allies is within 5 feet of the creature and the ally isn't incapacitated.
Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 23 (4d8 + 5) slashing damage. If the target is a creature with hit dice greater than d8s, the damage dice for this attack are equal to the target's highest hit dice. Rend. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 21 (3d10 + 5) slashing damage and the target must succeed on a DC 13 Dexterity saving throw or have their armor class reduced by 1, up to a maximum of 5. AC lost in this way are restored after a short or long rest.