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| 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.
|| Snipers stand in place and fire at you with much better aim than the other enemies. They can fire in any direction.
| 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.
|| 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.
| 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.
|| 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.
| 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 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
||Defense bot 2
| 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.
|| 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.
| 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.
|| 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.
| 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 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 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 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.
Click on a boss' name to go to their section of the walkthrough for a detailed strategy on how to defeat them.
| These defense cannons only appear right outside of the entrance to the first base. Each cannon will lob explosives at the ground in an arc. In order to have a clear and safe place to shoot the door to the base, you should destroy these cannons first.
|| The boss of the first base, you will have to destroy this single eye, which can launch a ring of fire down to the bottom of the screen, before you can advance to the waterfall beyond. But first, you will have to take out the four power cores and two sets of guns that protect it.
|Shadow Beast entrance
||Phantom image core
| This is the defense system of the entrance to the second base. It is capable of shooting fireballs from its mouth and two hands.
|| The boss of the second base is composed of two parts. Each instance creates phantom images that split up. It is only vulnerable to attack when the phantom images come back together. They release small bombs that can be shot down before they reach you.
|Heavily armored vehicle
| These vehicles roll onto the screen, stop about halfway, fire bullets for a few seconds, and then slowly continue to the left. They have limited firing range, and you cannot jump over them. You must shoot at them continuously in order to destroy them before they run you over.
|| The anti-gravity transport flies in at the end of Stage 5, and opens up to reveal a never-ending supply of soldiers who fly out to attack you. Bombs drop from the center. You must take the shuttle out to advance.
| You will face this hulking brute as you attempt to escape from Stage 6. He jumps around the screen and throws disk-like mines at you.
|| After fighting through jungle, bases, waterfalls, and snowfields, you will reach the literal heart of the alien territory. It fuels the cocoons of aliens that have yet to be born, and must be destroyed before the Red Falcon menace takes over the world.