Can Ugh-Zan IV be defeated at all on Serious difficulty at 400% health?

I wanted to try how the ultimate Serious Sam 3 tastes like, so I started the last level on Serious difficulty with infinite ammo and 400% enemy health, for a whopping ×57 multiplier. It's pretty serious and in the last few waves you just have to spam cannonballs (it's still more fun than your run of the mill 16 player coop where you're trying to engage some enemies that you can kill normally and people just spam cannons away for fun and profit).

Things went pretty nice (given that I was alone for pretty much 98% of the level) and I managed to survive enough to reach the final boss with over one million points (you lose 10k on death), then Ugh-Zan arrived.

Well, my use-one-bar-then-spam-cannons strategy didn't work so well, perhaps unsurprisingly. So I kept throwing bars at his behind. At the 5th bar, he stopped having room in his back for new bars, apparently. The boss fight loop then becomes:

1. Ugh-Zan goes for the sand whale, cannon spam to fight his regeneration is practically useless. He will have 100% health at the end of this phase.
2. Ugh-Zan turns around and celebrates, then five lightning bolts turn him to 20% health and regeneration stops. Cannon spam gets him to 5%, then he resumes.
3. Ugh-Zan engages you, and cannon-spam to fight his regen is again useless, because...
4. Ugh-Zan is again struck by five lightnings, but those lightning drop him at 20% health anyway, even if he had 60% to start with. They're just scripted that way. You have a little more time to strike this time around, and I got him to 1% at best. Then he resumes regenerating and I'm back to square one.

When another player joined the fight, things got worse as each cannonball now made less of a dent on the skin of this serious boss.

_{After a couple of cycles, he left. Then I noticed I'd died for the 40th time, and I was experiencing a very annoying glitch where I'd get sucked away from the battlefield into sand whale territory (land of the instantly overheating jet-pack), so I'd have to fall, get killed by mobs, respawn, get "instakilled" by the whale except I have respawn invulnerability, be stuck in place until I get killed again and then get respawned in the middle of the square. Cannon spam to fight his regen is pointless anyway, but being stuck like that is enraging, so I joined him in "ragequitting".}

Can Ugh-Zan be defeated at all on Serious difficulty and 400% strength? How many players are required? How many bars in the back are needed?

It is POSSIBLE...

Ugh-Zan IV can be defeated at 400% health. I personally decided to go out of my way, and actually buy the game and try it out for the sake of this question. I managed to beat him along with the help of 3 different expert players (names listed below) First of all, your strategies are not going to work if you try any ordinary strategy. We first decided to go along with your strategy and try to see if we could manage to beat him with a normal cannon-spam with something else, I can't quite remember. We quickly failed at this... Next, we tried to use an C-4 against him, but couldn't manage to land one, so that was a fail and a wipe.

We finally managed to do it by throwing about 7 poles into his back and after he was struck by lightning he was down to about a quarter of his max health. After that, the sand-whale came back and started wrestling him again. In this time, we managed to spam him with cannonballs. By the time, he was done wrestling the sand-whale, and the sand-whale had retreated once again, we did an all-out blitz with the poles, cannonballs, and rocket launcher. In the end, we managed to bring him down, so YES IT IS possible!

Players with me: OpenUpSweety, xxX_Jack***Hunter_Xxx, and UpandDownandUp