Spider Climb. The Xenomorph can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Alien Mind. The Xenomorph has advantage on Wisdom saving throws.

Devil's Sight. Magical darkness doesn't impede the monster’s darkvision.

Regeneration. The Xenomorph regains 10 hit points at the start of its turn. If the monster takes fire damage, this trait doesn't function at the start of the monster’s next turn.

Acid explosion. When the Xenomorph is reduced to 0 hit points, it explodes, and any creature within 10 feet of it must make a DC 13 Constitution saving throw. On a failed save, the creature takes 14 (4d6) acid damage.On a success, the creature takes half as much .

Fear Aura. Any beast or humanoid that starts its turn within 10 feet of the monster must succeed on a DC 16 Wisdom saving throw or be frightened until the start of the creature’s next turn.

Multiattack. The Xenomorph makes three attacks with its tentacle pincers or two with tentacle pincers and one with bite.

Poison Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 7 (2d6 + 8) poison damage plus 3 (2d6) piercing damage.

Tentacle Pincer. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 7 (1d6 + 4) bludgeoning damage plus 3 (1d6) piercing damage.

Acid Breath (Recharge 5-6). The monster exhales acid in a 60-foot line that is 10 feet wide . Each creature in that line must make a DC 18 Dexterity saving throw, taking 67 (10d8) acid damage on a failed save, or half as much damage on a successful one.

Grapple. It has advantage against grappling a target with it's tentacle. When an attempt of grapple is being made, target must succeed a strength saving throw DC of 18. On failure, the target is grappled ad must do a subsequent save each of it's turns if able. 

Sentinel:  When it hits a creature with an opportunity attack, the target's speed becomes 0 for the rest of the turn

The Xenomorph has 4 legendary actions.

Poison Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 7 (2d6 + 8) poison damage plus 3 (2d6) piercing damage.

Tentacle. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 7 (1d6 + 4) bludgeoning damage plus 3 (1d6) piercing damage.

Fear Aura. Any beast or humanoid that starts its turn within 10 feet of the monster must succeed on a DC 16 Wisdom saving throw or be frightened until the start of the creature’s next turn.

Movement. The Xenomorph can move equal it's walking speed without provoking opportunity attacks.