World 6-1
Nothing much here. Three humans, no collectibles and a few enemies.
World 6-2
Nothing much here either. Four humans this time, no collectibles and a few enemies.
World 6-3
Three humans here along with a decent amount of resistance. A Visitor (1/5) will arrive from the west going down, so keep an eye out for it if you're the type that collects everything.
World 6-4
You'll find a Beacon (1/3) in the northeast corner, as well as a Secret Human (1/5) trapped inside one of the canisters in the middle of the area. Save the three wandering humans before clearing all the enemies to complete the level.
World 6-5
Quick one here. Small area with only two humans, no collectibles and a few hostiles.
World 6-6
Destroy the glowing blue cansiter in the northwest section to rescue a Secret Human (2/5). A Visitor (2/5) will also come in from a spot nearby and travel southward. You'll also find an SP weapon box on the east edge of the platform.
World 6-7
Here we have five humans clustered pretty close together. A Secret Exit (1/3) is also hidden near the glowing blue canisters to the north.
Secret Level 1
Three humans to save, no collectibles and a considerable number of enemies. Defeat everything to proceed.
Secret Level 2
Four humans to save, no collectibles and a considerable number of enemies. Defeat everything to proceed.
Secret Level 3
Four humans to save, no collectibles and a considerable number of enemies. Defeat everything to proceed. You can also snag an Extra Life from one of the glowing blue canisters in middle-left section of the area.
Secret Level 4
Four humans to save, no collectibles and a considerable number of enemies. Defeat everything to proceed.
Secret Level 5
Four humans to save, no collectibles and a considerable number of enemies. Defeat everything to proceed.
Secret Level 6
Four humans to save, no collectibles and a considerable number of enemies. Defeat everything to proceed.
World 6-8
A Visitor (3/5) will emerge from the northwest corner not long after you arrive on this floor. There's not much else besides that here so defeat all the enemies to move on. Don't forget to grab the three wandering humans though.
World 6-9
There is a Secret Human (3/5) inside one of the glowing blue canisters to the northeast. Save the two other humans and defeat all the enemies to complete the level.
World 6-10
A Secret Exit (2/3) is hidden behind the middle section of the left wall. Rescue the four humans then clear the room to proceed.
Secret Level 7
Three humans to save, no collectibles and a considerable number of enemies. Defeat everything to continue.
World 6-11
There's a Secret Human (4/5) in the northeast corner of the level. A Visitor (4/5) will also come in from the north, closer to the left side. Grab the four other humans afterward before moving to complete the level.
World 6-12
A Beacon (2/3) stands far to the north away from the main platform. The final Visitor (5/5) will emerge from the northeast corner of the area as well. Rescue the five humans then clean up the hostiles to proceed.
World 6-13
The final Secret Human (5/5) is inside the glowing blue canister by the west wall. The final Beacon (3/3) stands in the southeast corner of the area.
Save the five humans then stand on the south end of the platform, and shoot left to find another Secret Exit (3/3).
Secret Level 8
Four humans to save, no collectibles and a considerable number of enemies. Defeat everything to proceed.
World 6-14
Grab the two humans and defeat the aliens to finish up quickly.
World 6-15
This is the last floor before the boss battle. There is not a lot of enemies here though, but most of them are big ones. In any case, grab the four humans and defeat all the enemies to make the boss appear.
World 6-16
This is the game's final boss so expect a tough battle ahead, unless of course you are really good at these kinds of games. Unfortunately I cannot offer much advice here other than to find gaps between all the different projectiles that the Supreme A.I. throws at you. These can be lasers and skulls coming at you fast at the same time. Do your best to react quickly and shoot the thing until you defeat it.
There is also points in the battle where the boss will box you inside some kind of trap. The beams that surround you will stay for a while, so try not to run into them as yo continue to attaack your opponent.