Xerannosaurus-Rex

Amphibious. The Xerannosaurus-Rex can breathe air and water.

Acidic Blood. A Xerannosaurus-Rex has a caustic blood like fluid that flows beneath its carapace.  A creature that deals bludgeoning, piercing, or slashing damage to the xenomorph while standing within 5 feet of it must make a DC 15 Dexterity saving throw, taking 18 (5d6) acid damage on a failed saving throw, or half as much acid damage on a successful one.  Additionally any creature that failed its save takes half as much damage on the following round.

Echolocation. The Xerannosaurus-Rex can’t use its blindsight while deafened.

Pack Tactics. The Xerannosaurus-Rex has advantage on an attack roll against a creature if at least one of the Xenomorph’s allies is within 5 feet of the creature and the ally isn’t incapacitated.

Darkness Camouflage. The Xerannosaurus-Rex has advantage on all Stealth checks when in Dim Light or Darkness.

Legendary Resistance (3/Day). If the Xerannosaurus-Rex fails a saving throw, it can choose to succeed instead.

Multiattack. The Xerannosaurus-Rex can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 15 (2d8 + 6) piercing damage plus 4 (1d8) acid damage.

Stomp. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 6) bludgeoning damage.

Tail. Melee Weapon Attack: +9 to hit, reach 15 ft., one target. Hit: 13 (2d4 + 6) bludgeoning damage.

Frightful Presence. Each creature of the Xerannosaurus-Rex's choice that is within 120 feet of the dragon 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 dragon's Frightful Presence for the next 24 hours.

Acid Breath (Recharge 5-6). The Xerannosaurus-Rex exhales acid in a 60-­foot line that is 5 feet wide. Each creature in that line must make a DC 18 Dexterity saving throw, taking 54 (12d8) acid damage on a failed save, or half as much damage on a successful one.

Hunter's Rush. If a creature leaves the Xerannosaurus-Rex's threatened area the Xerannosaurus-Rex can move with it and make an attack with it's stomp.

The Xerannosaurus-Rex can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The Xerannosaurus-Rex regains spent legendary actions at the start of its turn.

Detect. The Xerannosaurus-Rex makes a Wisdom (Perception) check.

Stomp Attack. The Xerannosaurus-Rex makes a Stomp attack.

Tail Sweep (Costs 2 Actions). The Xerannosaurus-Rex swings it's tail around itself. Each creature within 10 feet of the Xerannosaurus-Rex must succeed on a DC 19 Dexterity saving throw or take 13 (2d6 + 6) bludgeoning damage and be knocked prone.

Roar (Costs 2 Actions). The Xerannosaurus-Rex lets out an ultrasonic screech.  All living creatures other than Aberrations within 30 feet of the Xerannosaurus-Rex must make a DC 18 CON saving throw or be Deafened.  A deafened creature can make a new Saving Throw every round at the start of their turn to end this condition.  

Summon Warriors (Costs 2 Actions). The Xerannosaurus-Rex lets out an screech.  This summons 2d4 Xenomorphs who arrive and act at the beginning of the next round.