I recently started working through the gold class challenges and finally got Berserker Gold. I thought I'd post my strategy to see if I didn't miss a way to make it easier. If not, I thought I'd throw up a page on the wiki for that challenge.
The key to this challenge is that you'll need to assemble a huge fireball spike to kill the last boss, who has huge physical resistance and a giant boatload of HP. Everything you do is focused on improving this spike.
Worship Mystera ASAP (the altar always spawns near the stairs) and find a glyph as soon as you can. It's important to turn every point of mana into Mystera piety as soon as possible, even if you're just poisoning monsters you have no intention of fighting. (If you explore a good chunk of the dungeon and don't find a glyph at all, restart.) Mystic Balance is the highest priority; you'll also want two hits of Magic, Refreshment, and (immediately before engaging the final boss) Flames.
Try not to convert more glyphs than you have to before fighting the boss, since you'll want to take advantage of Refreshment for bonus mana.
Before engaging the boss, take Consensus if you need it followed by Alchemist's Pact to provide a mid-fight level up. (I considered taking Spirit Pact for an extra mana potion, but I think the level up is more helpful.)
All of the monsters are melee-unfriendly. Doom Armors are the easiest to take down above your level, using the familiar trick of fireballing them to remove one death protection and then attacking another monster to remove a second. Don't be afraid to use health potions to beat ordinary monsters; they won't help you against the boss. Likewise, don't be afraid to take a couple stacks of Weakening from the succubi, and don't be afraid to get cursed, since your resistance won't help anything anyway.
Your item purchases should be things that improve your spellcasting; the Pendant of Mana, Battlemage Ring, Crystal Ball, and Dragon Soul are ideal. Whrargbl is surprisingly helpful since it lets you continue to stack Burning as you are fireballing a monster or the boss.
As you fight the boss, your Burning stacks can get very high, and this provides a significant fraction of your damage. Fighting monsters for a mid-fight level up will cost you your Burning stack, which is why the Alchemist's Pact is good (and don't quaff a Schadenfreude until you have to, unless you have Whrargbl to not lose your Burning stack.)
I don't know what effect the Piercing Wand would have on this dungeon. It seems like it would help a lot; at the very least, you would get one good physical swing in for significant damage and if you had your health potions left, you could get another.