AlienCruise

Story-related; cannot be missed.

This planet is just right of the big pink planet. The first stage is really simple; grab the shotgun and you should make short work of all enemies. The second stage is just a miniboss fight against a bee. Stay to the far left and your shotgun will make short work of it. The third stage is also very straightforward with nothing tricky. As mentioned in the roadmap, I recommend avoiding the weapon powerup and sticking with the shotgun.

The boss fight is pretty easy. You need to shoot the bug in its mouth between the two pincers. It'll shoot out various projectiles, but they can all be destroyed. Rocks will fall, but indicators pop up on screen letting you know where they're about to fall from. Its only other attack is shooting a laser at you, which is easy to avoid by just staying near the boss and going to the opposite end of the screen (top or bottom, depending on where the laser starts). The shotgun will tear through its projectiles and do tons of damage, so if you kept it this should be a quick and easy fight.