A good list of xenomorphs and their variants
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http://aliens.wikia.com/wiki/Xenomorph


Ideas for me would be a few traits for non xenomorphs.

Traits:
Cult of Devourer
Benefit: Xenomorphs are non hostile to you unless attacked.
Feats:
Xeno Cultist
Prerequisites:Cult of Devourer Trait, manifester or caster level 1.
Benefit:You Gain the Hive Mind Trait.

Defiler
Prerequisite:Cult of the Devourer trait, Xeno Cultist feat
Benefit: As a standard action you may create a Node as the Drone ability. You can use this ability once per day.The Node must be placed near organic matter to survive.
Grand Defiler
Prerequisite:Cult of the Devourer trait, Xeno Cultist feat, Defiler feat.
Benefit:You gain a extra use of the Node ability granted by the Defiler feat.

Familiar of the Hive
Prerequisites:Cult of the Devourer trait, Xeno Cultist feat, Caster level 4.
Benefit:You gain a advanced Chestburster who does not advance into a Warrior or Drone. The Advanced Chestburster is treated as a familiar of your level.

These are for non Xenomorphs and I'll put the reason why in spoilers.
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In the Iron Kingdom setting they made tribute to the Predators as a species unknown to the entire world except those they hunt, once they make the kill the essentially take their trophy which is usually the head. I'm tossing these feats out as possible anti-xenomorphs

Great Hunter
Benefit:+2 to all damage rolls against aberrations.

Predator Taught
Benefit:You gain a +2 bonus to all attack and damage rolls

Predator Survivor
Benefit:Survival is now a class skill, if it is already a class skill you gain a +2 to all survival and Knowledge(*Geography)

Xeno Hunter
Prerequisites: Favored Enemy(Aberrations)
Benefit: All attacks against Xenomorphs gain a +4 bonus to damage.
Xeno Killer
Prerequisite:Rage Class Feature, Predator Taught trait
Benefit: When using Rage you gain a +2 bonus to attack and damage rolls against all aberrations.