Acidic Blood. Xenomorphs have acid blood, which has notable affects on combat. If a Xenomorph takes slashing or piercing damage, blood sprays out five feet in the direction of the hit. This takes the form of a thin cone. Anything within this cone must make a DC 15 Dexterity saving throw. On a failed save, the creature takes 11 (4d4+3) acid damage, or half as much on a passed save. Additionally any creature that failed its save takes half as much damage on the following round. There are two other traits of their blood. The first is that it is to acidic for diseases to develop in the creature's body. The second is that it works as a potent antivenom.

Lethal Ambush. When the Xenomorph attacks and hits a surprised creature with a melee weapon attack, the final damage of the attack is tripled.

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

Pack Tactics. The Xenomorph 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.

Enrage. Whenever this creature looses half of its health, it goes into a rage. This rage has the following effects:

• Advantage on all melee attack rolls
• Resistance to bludgeoning, slashing, and piercing damage from non magical means
• The ability to dash as a bonus action

No Eyed Predator. Xenomorphs are creatures that do not actually have eyes, and are technically always blinded. They instead see via echolocation. This also means that they effectively have a form of truesight, darkvision and blindsight when not deafened. When deafened, they are effectively both blinded and deafened.

Thick Carapace. Xenomorphs have a very thick carapace designed to keep them safe from attacks by other member of their own species or similar creatures. The carapace has the following attributes:

• Completely acid retardant
• Highly Flammable
• Highly cold retardant

"Hive Mind". Xenomorphs don't have a proper hive mind, but they do have something very similar. This sort of "shared consciousness" has two highly notable effects on the xenomorph. The first is that they don't have a proper fear response, which does not mean they don't have the flight part of fight or flight, just that they can't be frightened. The other aspect is that they can telepathically communicate with members of their family group from great distances away. It has been found to be possible to sever this connection, it is just quite difficult, and will result in the creature behaving more like feral dog than anything. (If the connection is broken, they lose the fear immunity and telepathy, but they become tameable with a high enough handle animal check.)

Careful Prowler. Xenomorphs are unaffected by difficult terrain. (With the exception of situations where they have to swim.)

Multiattack. The Xenomorph can do a multiattack that consists of: 2 claw attacks, 1 bite attack, and either 1 tail attack or 1 tail swipe attack. It this multiattack grapples the target, they can't do a tail swipe, but can add a proboscis attack with their bonus action.

Claws. Melee Weapon Attack: +5 to hit, reach 5 ft., 1 target. Hit:  7 (1d6 + 4) slashing damage. Any creature hit by the Xenomorph's Claws must make a DC 14 Dexterity check or be grappled. A grappled foe is automatically released after one minute.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., 1 target. Hit: 10 (1d8 + 6) piercing damage. 

Tail. Melee Weapon Attack: +5 to hit, reach 10 ft., 1 target. Hit: 6 (1d12 ) Piercing damage. 

Tail Swipe. Melee Weapon Attack: +5 to hit, reach 5 ft., up to 5 targets. Hit: 7 (1d6 + 4) slashing damage.  The tail is swung in an arc that hits targets to the left and right, diagonal left and right in front, and straight in front of the creature all at once.

Acid Spit. Ranged Weapon Attack: +5 to hit, range 20/60 ft., 1 target. Hit: 8 (1d4 + 6) Acid damage. Since this attack is the Xenomorph spitting a glob of its own blood at the target, the target has to make a DC 15 Constitution save. On a failed save, they take half the initial hits acid damage at the end of both the current and next round, on a passed save, they take no additional damage.

Proboscis. Melee Weapon Attack:  As a Bonus Action the Xenomorph can extend a proboscis, complete with secondary jaws, to strike a Grappled creature.  This deals 10 (1d8+6) points of Piercing damage PLUS 7 (2d6) points of Acid damage.  

Feral Strike. Whenever a xenomorph is hit by a non-magical attack, it can use a reaction to do a tail attack at the nearest individual within range.

Screech. When a xenomorph is hit by any attack, it can use a reaction to let out a bone chilling screech. Any creature within a 40 ft radius of the screeching xenomorph must make a DC 15 constitution saving throw. Pass or not, anything within the area takes 1d4 thunder damage, but any creature that fails this save are deafened for the next minute. Other Xenomorphs are not affected by the screech.