This boss is insane. I've got a jetpack and some steel rods. WTF am I supposed to do? Killing enemies just respawns more enemies, and I can't kill the boss with conventional weapons since he recharges... I have no clue what to do.
Got it. Apparently you have to just kill stuff until the sand worm fights the boss and you can get the rods into his back. Only figured that out by reading the steam forums... Not sure how you're supposed to just know that. There was no indication that you had to get his back at all... Kind of a low point on an otherwise decent game... And holy crap that last level had a lot of enemies lol ;)
You don't really need to kill stuff for the sandworm to appear, just drag the boss to the sandy area and it will eventually happen. It's an easy fight overall. I ignored all the enemies and just focused on the boss. I think you don't get points for fighting infinite spawning enemies during bosses anyway.
The only thing that made it difficult was how erratic the jetpack is. Sometimes it would overheat suddenly for no reason, and if you touch the sand, you'll be swallowed by the worm immediately. Even if you can land near the temples, sometimes it just won't cool down. The only reason I had to try the battle so many times was due to the jetpack, otherwise, it's very easy. Just stick the rod, wait until the lightning hits, and pound away with the cannon. Repeat if you can't quite kill it the first time.
I think the jetpack suddenly overheats like that if you get too far from the ruins area. Most of that time when that happened to me, it only happened if I went in a certain direction from where I was, and if I didn't get killed by rockets, I got eaten by a sandworm moments later.
I don't know, it happened to me a few times even when I was near the center area. If I managed to land on the center (so as not to get swallowed), the jetpack still wouldn't cool down anyway. The only way to make it work is to make sure you land before it gets too hot, in that case it will cool down relatively quickly.