Marine

Not long after what happen in Aliens, a scientist comes to LV-426 to study the Xenomorph, but His excavation is wiped out. He survives and finds He can study Xeno's on another planet, so He goes ther and set's up a installation, and begen's his studies, Marines show up to capture him, (I forgot his charges) But They axcidently let the Xenomorphes loose, but that's not all, This planets a favord hunting ground for Predator's!

Alien

A smuggler Axcidently drops a live Alien egg while (of coures) smuggling them, The egg goes in an airvent, It hatches, starting the first level, The objective would be to find a host. (which is a scientist) The next level Has a chest Burster being born, it's objective is to grow and survive, once it's fully grown, It's objective is to destroy the human intruder's of the planet.

Predator

While Hunting with his hunting party Marines ambush and kill two Preds. (I do belive they where freinds) His objective is to destory the marines and hunt.

(Note: Both Marine and Predator has a boss to defeat before the game ends, Of coures, The alien queen