"Each one of these things comes from an egg, right?" Ripley asks Bishop in James Cameron's Aliens. "So who's laying these eggs?"
"I'm not sure," Bishop replies. "It must be something we haven't seen yet."
Origins: Cameron's 1986 sequel to Ridley Scott's sci-fi horror classic increases the scope considerably. Instead of one, lone Xenomorph stowing away on board a ship, there's an entire planet full of them, having formed a hive amid the colonists there and creating countless numbers of swarming aliens. To stop them, we have Colonial Marines, "very tough hombres" who specialize in just this kind of thing - and who nonetheless find themselves extremely out of their depth. Especially when they face off against the queen that has been laying the eggs that produce the Xenomorphs in the first place.
Why So Powerful? Well, for starters, the alien queen is huge, towering over Ripley and the other survivors. The puppet used to bring the queen to life in several scenes stood more than 14 feet tall, with two human puppeteers inside and several others working from the outside to get all the parts to move. And she boasts all the same lethal traits that make the other Xenomorphs so dangerous, from a barbed, whipping tail to acidic blood and a second pair of jaws that jut out of her mouth. What really makes the queen alien dangerous, though, is her ability to lay those aforementioned eggs, which hatch into facehuggers, which can lead to more Xenomorphs, and so on.
Any Weaknesses? The Xenomorphs are all pretty sturdy, but when you get right down to it they can be damaged by anything that will damage a human - sometimes it just needs to pack a little extra punch. Ultimately, though, the queen is kicked out of an airlock into deep space, just like the primary antagonist in the first Alien film.