I only ever play as the alien, and I manage well enough even against auto targeting weapons, being spawn killed as a chestburster, etc. In most of the games I've played I can still run the other races ragged despite all their fancy weapons. Here are a few of the tactics I've used to dominate multiplayer games!
Successful alien play is all about making full use of its unique abilities - apart from launching an attack on a player below, I aliens should rarely touch the floor unless they absolutely have to. I can't stress this enough - USE THE WALLWALKING! Spend a lot of time on the ceilings in dark corners and ambush - many people I've played against are used to games where you don't need to look up, so often don't look for an attack coming from up there! I know it can be confusing to some people when running around all over the walls, practice offline running around a map without touching the floor!
Another tactic to use as alien is to sneak up on 2 antagonists duking it out, they are often so involved in their own fight they don't notice a creeping alien - it's a good way to get 2 kills in quick succession! Same goes for if you are a facehugger, remember you are small and fast, picking a target that is intent upon something else is a nice easy kill! Stealth is the alien's best weapon, after all, you have no ranged attack, and everything has to be up close and personal! Nothing more humiliating than rushing in on the ground only to die at your target's feet!
Sticking to walls just over doorways then as someone comes through, dropping onto them is a good way to pick up a headbite or two, especially on well populated maps. Make use too of the taunt key - aliens hiss, and it can mislead those hearing it, not to mention it's quite scary for non-alien players. A scared player will make mistakes in his panic! Make extensive use of ducts and vents, and know where escape routes are on the map - these are places you often can't be followed through - more of the map is available to you as an alien than any other species.
Using the pounce, not only for killing, but also for getting around the map, or making a fast escape is also useful. Used in conjunction with wallwalk you can leap quickly to ceilings and walls, even bounce from wall to wall as they did in Aliens. This I find confuses other players and makes them waste ammo. Another thing I noticed was you can break weapons, armour and health kits lying on the ground, denying them to the humans and preds!
And yes, the exosuits - 1 headbite will take them out completely! Only found this out by accident, when I cornered my friend in one and my inner jaws shot out!
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