THE REGULARS ALIENS
It is the first kind of alien you will encounter in the game. They are running fast, jump above obstacles and can easily climb on roofs. But they can only attack with their claws so you have some time to take them down before they reach you !
THE SPITTERS ALIENS
They are slowly and they crawl but they spit dangerous balls of acid which hurt over a small radius. Since they are attacking from a medium range, consider the hunting rifle or the revolver to accurately take them down. Be aware that once killed they explode into a large spit of acid !
THE WALKERS ALIENS
They are massive aliens walking with a heavy noise. They are slowly but require a lot of fire power to take them down. Explosives or shotgun shells are suited against them.
If you are running out of ammo in front of them, you will be in troubles because they can also climb on roofs !
THE ALIEN BOSSES
They are massively oversized and deadly ! They come once you defeat many alien waves. You better be well armed with a lot of ammo to counter them !