Ok so progress is suddenly slow, but i believe i may have made a breakthrough!
Last mook to be added. c:
Maybe not to correct scale, but i like the idea of the aliens getting really fucking serious after level 15. So, the Leviathan, as it's called for now, is a mostly classic snaky ship. It'll either swipe across the screen in a sinuous motion, or pop out in a parabolic arc for a quick potshot. Given the size of the ship, this potshot is likely a very big potshot.
Also, the middle sections are covered by deflector shields on their sides, so it is REALLY DIFFICULT to kill it by shooting those. The tail end can be shot up, but it won't destroy the entire Leviathan. To do that, you'll have to destroy its head, because smashing a middle section will just destroy everything BEHIND it, but not in front of it. Destroying the head of an otherwise intact Leviathan will thus result in a moderately spectacular chain reaction, although you're still at a slight risk of the remaining sections crashing into you before exploding.
And, speaking of collisions, being rammed by the Leviathan is likely to be fatal, and running into the side of it hurts a lot, given the deflector shields. The head itself is more or less MADE for smashing through smaller ships, so dodging it would be very wise indeed. On top of that, the head is also pretty tough to destroy, but less so than the middle sections. Since the Leviathan might well be an elite mook that keeps harassing you until you destroy it, the toughness of the head will make it difficult to destroy quickly without super shots. The tail is probably more fragile, and destroying it will at least free you from the potshot that it keeps taking at you, but not the risk of being rammed, which it might attempt more aggressively if you manage to destroy the tail gun.
So yeah, that's the Leviathan. Very dangerous, high priority target, fitting for the last few levels. Just so you don't get too comfortable in your super powerful space ride. ;o
also yes it's partly inspired by Beat HazardSO NOW, the only two concepts left are the last "other upgrade" and the final boss. The boss is for a later update, though, so yeah.