Has anyone defeated Belranga, and if so how and are the benefits worth the effort?

I'm playing my 2nd game on Veteran, and thought I'd do ok w/ my normal band of 20th level PCs, but I kept getting wiped. So I did some internet searches to find various strategies and builds/gear etc. that have worked. And yes, there is 1 of 2 unique drops that make the fight worth winning, beyond bragging rights--a mythical upgrade (I had assumed legendary was the top level until now).

Watcher: Fighter, but acted more like a tank for much of the fight.
Eder: Swashbuckler, using the Animancer's Energy Blade (Raw dmg so doesn't worry about Penetration); Blackened Plate Armor w/ the upgrade that lowers an enemy's Armor Rating by 1.
Xoti: you'll obviously need her healing etc. She wore a Bone Setter's Torc (3 charges of removing all Injuries etc.)
Konstantin: I didn't do this, but re-speccing him if need be to get the 8th tier ability "With all your Strength, Slay the Beast" (+20 Accuracy, +30% dmg) would have been a good idea! But I kept him firing away w/ the hunting bow that does extra dmg b/c he's a dwarf, and summoning creatures (drakes and weapons mainly).
Maia: the arquebus Red Hand (shorter range but 2 shots at a time).

There are other items that give +Accuracy > Beasts of course. Important are the best healing potions, and Luminous Adra potions (remove injuries) for the 2 melee types near her. Once she gets down to 75% health, you have to start worrying about Consume attacks that give 1-2 Injuries. There's a animation windup that tips you off and you're supposed to run away (taking a Disengagement attack is much preferable), but I was so busy focusing on other things, I never could avoid those attacks. But between a few L. Adra potions and that Bone Setter's Torc, I survived.

The thing to keep in mind is that Belranga is almost invincible early on, as you'll see when you try to hit or damage her. Her defenses are ridiculously high. The trick is to start lowering her defenses by killing spider minions, but the danger is that her offense gets better when that happens. The sweet spot is probably between 60-70 minions and then try to take her down quickly. KEY: the soulblade dagger's ability that automatically kills (1/rest) anything (!) w/ less than 25% health. That little dagger's been Eder's mainstay weapon for much of the game, and I switched to it as soon as I could.

Her normal AR is 15, but only 8 v Crush/Corrode. I didn't use any crushing or corrosive attacks; just an example of another way to whittle her down (once her defenses are in the normal realm). Different things will work, just be patient. I held off on summoning from items for a good while. Also, items or food that prevent being paralyzed (Dex affliction) are crucial for at least the 2 melee types (Shark's soup for Eder).

This is just what worked for me; other companions and builds can work too if you do a little searching. Quite the challenge! Now I'll go get spanked on the newer megaboss (the ooze) and try to figure out who and what I need to beat it...

Well, 3rd game on Veteran, and I had a much, much harder time. No thanks to the increased Veteran difficulty. I wasted half the day before settling on a winning strategy/team, and it still took multiple tries. What annoys me is that there are 4 locked Achievements--I assumed for the 4 megabosses now in the game--but no Achievement generated when I finally beat Belranga. Sigh.

Watcher: Hunter w/ upgraded (+2 PEN) St. Omaku's Mercy; Horns of the Bleak Mother (+10 v Beasts); Spider Silk Robe (I think for no recovery); and some potions that never came into play. All 5 PCs had AI turned off so there was lots of micro-management.

Pallegina (Herald): switched to Chromoprismatic Q. staff (Belranga had 10 AR v Crush by default); a L. Adra potion for those hard to avoid Consume attacks that impart Injuries; potions of Major & Mircaulous Healing; 3 Animated Weapons whenever I could summon them!

Eder (Swashbuckler): Blackenened Plate Armor (upgraded to reduce AR by 1 of enemies engaged); Animancer's Energy Blade (could have used a blunt weapon but I was pretty damn quick w/ this)--switching to Marux Amanth when the boss was < 25% health for the deathblow, of course; same potions as Pallegina.

Xoti: Bone Setter's Torc (allowed me to remove Injuries 3x); scepter Amaliorra; scrolls of Major Healing; a scroll of Hand of Weal & Woe; and 3 scrolls of Revive the Fallen.

Konstanten: the key to surviving this stupid fight. Had the 8th level phrase that gives +20 Accuracy & +30% dmg against Beasts; summoned 4 Animated Weapons whenever possible; scepter Current's Rush.

Everyone had a Figurine to use to buy precious time; all but Pallegina rested w/ K. Tea (immune to poison); as she was immune already, I just gave her a +1 PEN food item (T. Snapper).

All in all a ridiculous fight on Veteran difficulty now. I might not be tempted to try it again in future games, especially b/c I didn't even get an Achievement for it. If I'm feeling masochistic, I'll check out the other 3; the massive ooze already gave me fits in my 2nd game and I ragequit after a while. LOL.

Hope this is helpful.