Soldier

Soldiers run across the screen and jump when they reach a ledge. They may fire bullets at you occasionally. In bases, they run or jump across the background, stopping to shoot at you before they leave.

Sniper

Snipers stand in place and fire at you with much better aim than the other enemies. They can fire in any direction.

Scuba Soldier

They attack by firing a shell into the air that splits into three pieces before it hits the ground. It is difficult if not impossible to kill these guys. However, they can only fire directly upwards, so their bombs are usually easy to avoid.

Gunner

Gunners attack from stationary cannons that fire large bullets at you. The bullets are fast, but the gunner pauses after firing three shots, giving you time to move into position. You can avoid getting shot by crouching.

Wall turret

Gray boxes with a rotating cannon are very common in the first half of the game. They're quite easy to destroy since they have a limited number of firing directions. They're initially inactive but when you get close to them, they'll activate and start firing at you.

Cannon

Cannons pop out of the ground when you are within firing range. They can only fire ahead, and you are safe shooting at them when you crouch because their bullets fly over you.

Wall Turret

Stationary guns with a red light on top appear in almost every room in the bases. They fire only occasionally but combined with all the other things that'll appear in any given room, they can be a challenge to avoid.

Mines

Mines will slowly roll toward you from the back of the rooms, sometimes in a line, but usually randomly. You can jump over them with good timing, but it's usually easier to duck and destroy them with a few shots. They can also be tossed by soldiers as they run across the back of the screen.

Defense bot 1

White defense bots appear when you invade the power core of the second base. They run out from the sides, and leap down to stop you. Destroy them before they reach the floor.

Defense bot 2

Red defense bots also appear when the white bots do. However, instead of leaping down to the floor, they stay above and shoot at you in an effort to disrupt your assault on the core.

Alien head

This head appears near the beginning of the alien base. It's only attack is to spit out Floaters. Push yourself against the wall to the right and fire diagonally upward to hit the mouth.

Floaters

Floating aliens slowly move around and try to run into you; they have no other form of attack. They're easily destroyed, but be sure to take them out quickly, as larger numbers can overwhelm you.

Alien mouths

The alien version of a turret, it is attached to floors and ceilings and attack by creating spores that home in on you rather quickly if you don't destroy them. They are stationary, but take a few shots to destroy.

Spores

Spores are smaller than floaters, and they are much faster. They travel straight for you, and typically end up moving into your line of fire. Watch out for the few that slip by.

Egg hatch

Egg hatches release baby aliens in the form of Crawlers. They must be destroyed in order to prevent further Crawlers from appearing and interfering with you mission.

Crawlers

Crawlers hop out of the hatches and run along the floor to reach you, or run across the ceiling and dive down at you. They will defend the heart that feeds the alien base with their lives.

Alien head

This head appears near the beginning of the alien base. It's only attack is to spit out Floaters. Push yourself against the wall to the right and fire diagonally upward to hit the mouth.

Floaters

Floating aliens slowly move around and try to run into you; they have no other form of attack. They're easily destroyed, but be sure to take them out quickly, as larger numbers can overwhelm you.

Alien mouths

The alien version of a turret, it is attached to floors and ceilings and attack by creating spores that home in on you rather quickly if you don't destroy them. They are stationary, but take a few shots to destroy.

Spores

Spores are smaller than floaters, and they are much faster. They travel straight for you, and typically end up moving into your line of fire. Watch out for the few that slip by.

Egg hatch

Egg hatches release baby aliens in the form of Crawlers. They must be destroyed in order to prevent further Crawlers from appearing and interfering with you mission.

Crawlers

Crawlers hop out of the hatches and run along the floor to reach you, or run across the ceiling and dive down at you. They will defend the heart that feeds the alien base with their lives.

Egg hatch

Egg hatches release baby aliens in the form of Crawlers. They must be destroyed in order to prevent further Crawlers from appearing and interfering with you mission.

Crawlers

Crawlers hop out of the hatches and run along the floor to reach you, or run across the ceiling and dive down at you. They will defend the heart that feeds the alien base with their lives.