This is a tough level, as it is almost entirely mini-bosses. While you are not fighting a mini-boss you have some annoying little spiders and some things in the ceiling that drop columns of purple goop to deal with. Watch out for the spiders' lasers – they ricochet off the walls. Throughout this level there are sometimes some items stuck in hard-to-reach nooks and crannies, but don't bother trying to get them unless they are a 1-up, probe, shield, or Hunter. It is most likely that you will either get stuck in the hole and die or run into the wall and die.
The first mini-boss is a large black ball that will bounce around the room. It will first advance slowly, then open up and fire a miniature rocket-powered version of itself at you along with two lasers. If you can use the Thunder Sword, use it right when he opens, then motor out of the way of its shots. Avoid the ball as it bounces around the room and blast its core when it opens to fire at you. After this mini-boss there are two routes to take for the rest of the level, a top mini-boss or a bottom one. They are always almost the same boss but with different attacks. The first mini-boss for this level is a bit more difficult, and you should take the bottom course.
You will end up in a room with three alien dispensers mounted on the ceiling. You must destroy all three dispensers to win this fight. The aliens that are dropped from the dispensers will walk around and fire lasers at you. Do not try to kill the aliens, because their heads will fly up and pose an even greater threat. Also, don't get hit by the junk that falls out of the busted dispensers. This time take the top mini-boss. This mini-boss isn't too difficult, and as long as you keep firing at him, most of his attacks are easily avoided except for an attack when he fires a blast similar to the Thunder Sword from his fist. He can do this quickly and without warning, so be careful.
You should take the bottom mini-boss next, and you will encounter the core from the first mini-boss of the level along with some buddies. They form a snake that will first move toward you and then swing their tail around so they face the other direction. They will then swing their tail forward, twist around, and fire several lasers at you. They then repeat the same process so they end up in front of you again. They are fairly easy as long as you don't get hit when they swing their tails around. Notice that when they opens their mandibles to fire lasers at you, their head darkens in color. This is the only time you can hurt them, so take advantage of every opportunity you get.
The boss of this level, Evil Core, is the second-hardest boss in the game, so be prepared for trouble. First, two fuzzy insect arms will reach out and shoot little flies at you. The arms themselves aren't that dangerous, but the little flies will fall and explode when you kill them, sending up a steam cloud that can force you into the ceiling, killing you. If you can't avoid one of these clouds, press 
to avoid getting smashed into the ceiling. Shoot the purple spots on the arms to destroy them. Once both arms are gone, the little insect-thing inside the egg will come out, and a whole bunch of those flies will come and pick it up. The best strategy here is to use Freeway or Hunter if you can, and use them to shoot at the bug and flies, killing them in concentrated groups. Then move out from above the falling flies to avoid the steam clouds. If the flies do manage to pick up the insect-thing, he will drop and shoot to the left and right, so watch out. After receiving enough damage, the insect-thing will call a huge bee to come and carry it. The bee shoots lasers at you, and the insect-thing will drop huge globs of acid spit that have the same effect as the flies dropping. Shoot down the bee and insect-thing down, and then get as far behind the insect-thing as you can. It will start spewing those little flies all over the place and the only safe spot is behind it. When it explodes, you will be flung into the next level by an enormous explosion.