A Strategy Guide

Aliens (general): Always attack the head's of humans. Use stealth whenever possible. Never be predictable in your movements (i.e. don't travel in a straight line). Humans are much more effective in groups so target loners and cull stragglers whenever possible. With regeneration you never need to return to your base so use hit and run tactics to stay alive. If you're outclassed wait until your defensive structures weaken humans first or use a booster to poison.

Versus Turrets: Turrets won't try to fire through each other or other objects, so position yourself where the least amount of turrets will hit you. Focus on one turret at a time and back off once it stops firing because it'll explode soon and deal splash damage to players and to other structures. If you have room to maneuver, strafe back and forth or all around a turret while slashing since they aim very slowly. You can do this on top of turrets as well. If all you need is to get past a turret front, you can sacrifice a dretch to draw their aim somewhere convenient so you'll have more time to get by with your next life.

Versus Human Bases: Remember, the object of the game is to destroy the enemy base and then wipe out the survivors, so only focus on individual humans when you're in need of frags, or waiting for teammates to stockpile frags. In smaller games it's often possible to sneak into an improperly defended base and do significant damage, even with low classes. Look for a path through the automated defenses to the reactor or armoury. If you can take out the reactor before any humans realize what's happening then all the other defenses will halt and it becomes trivial to clean up the rest of the base. Attacking a reactor from above makes it much more difficult for turrets to target you and you'll take less damage from the reactor itself. If the humans are relying heavily on tesla generators try to take out the defense computer to render them useless. Even just a few quick hits can be used to take out an armoury, and doing so can seriously hinder a human team. In larger games, taking down automated defense is usually a bigger help for your teammates.

Dretch: You're silent when moving so find a hiding spot and wait for a human to pass, then follow for a surprise attack. Stay on the ground and aim upward for safer headshots. The only structures you can damage are turrets and teslas, so if a human lays one down destroy them before they finish building, then kill the builder. Once spotted by a human use your wall walking to evade enemy fire until they have to reload, then go in for the kill. If you're outclassed, use poison or wait outside your base for humans to take damage from your defensive structures before attacking. Dretches actually have the highest movement speed in the game so unless one of the higher class's movement abilities would make getting to your destination faster it may be better to travel as a dretch and evolve when you get there. Dretches also have the fastest relative regeneration rate of all aliens besides the tyrant, so if you're damaged before evolving, wait until your health maxes out first.

Basilisk: Always focus on a single target. Use the grab to stick a human then jump on their head for a faster kill. The grab only works when actually aiming at a target. Be very careful of battlesuits and squads. Avoid turrets in groups of two or more. The grab will actually slow turret rotation speed so you don't need to strafe as much to kill single turrets. The gas is best used as a hit and run attack since it's fairly unreliable.

Marauder: Hit and run by jumping over humans and slashing at their heads. Never stand still. The slash can do more damage than the lightning, so only use the lightning to finish off near-dead targets. Avoiding chaining the lightning since the damage will be divided between all targets. Don't waste time attacking turrets when you can simply jump over them to reach vital structures.

Dragoon: Aim upward with a charged pounce to fly further. Only use the bite in close quarters when you can get a clean headshot. Use the pounce at all other times. The pounce doesn't do locational damage so you don't need to aim for heads, but do aim -- you can deal pounce damage without actually touching a human. Never bite mid-pounce, it will cancel the pounce damage. Always use the pounce for movement. You don't have to be on the ground to charge up the pounce, so press the button again immediately after releasing it. Use the barbs to snipe at enemy defense; target armouries first, then teles if they're vulnerable, then turrets. If the enemy is relying heavily on tesla generators take out the defense computer to cripple their base.

Tyrant: Your base movement is slow so don't go anywhere that's wide open or hard to maneuver in. Always use the trample to increase your speed. Kill or force a retreat on every human that could pursue you (remember to slash their heads). Retreat from pursuers only to regain health and set up an ambush. You can take out turrets easily and absorb fire from one or two simultaneously, so don't be afraid of them. Be careful of backpeddling or circle-strafing humans with powerful weapons (like the chaingun or lucifer cannon) or distant humans with accurate weapons (like the mass driver). Use the trample to damage teleporters and medistations, since you can hit them while moving and its difficult to slash them directly. If you're regrouping with teammates stand next to them to double their regeneration rate.