The raven is the name given to a giant form of xenomorph. Rumored to be a cross between a basic warrior and a lurker xeno, its origins are very vague. The raven is very large and covered in an almost impenetrable, spikey carapace that is tinted red. For this reason it can only be killed with a powerloader.
It has the abilities of both of the aliens that it is "crosses" with, but its large size keeps it from climbing in vents. Its weight presumably stops it from climbing walls and ceilings too.
Most xenos prefer stealth when engaging marines but the raven will charge and give chase to even groups of armoured marines.
Another unique feature is its visible and evil looking eyes.
Even for a xenomorph, the raven is extremely aggressive. Pouncing on anything and everything on sight then cocooning them for later, to breed more xenos. It has been shown to attack other xenos in the area, possibly showing a mutated or slightly insane side to its behavior.
The raven has a level of strength that is unmatched by nearly all aliens. Most of its attacks are capable of killing a human marine in one hit and it can smash welded doors down on its own.
Whilst many xenos produce various hissing noises and other high pitched shrieks the raven possesses a loud and unique roar.