All unlocked monsters plus:
Naga: Weakening Blow
The boss is Ssseth ( Naga icon, Attack 90, Health 570, Weakening Blow, Physical Resist 95%, Magic Resist 95%).
The high resistances of the boss - as well as the fixed deity choice - makes this dungeon rather difficult to win consistently. By going in with the Gnome Paladin, you have an outstanding Mana spike against the boss, as the combination of (and ) plus your Mana Potions allows for an easy 100-150 Mana for the final fight. If you choose the Halfling Paladin, your spike is a bit more balanced, with a little bit more Health at the expense of some Mana. Gnome offers a bit more versatility as you can switch over to BURNDAYRAZ more easily, but Halfling offers a bit more resilience going in.
If you can couple your spike with a level-up, you should have ample resources to battle Ssseth. However, it will become a critical element to reduce his resistances. Chaining BYSSEPS and HALPMEH and/or Health Potions will wear him down, although this is fairly Mana intensive, plus the layers of Weakness he inflicts makes meaningfully damaging him harder towards the end. So either purchase a Fortitude Tonic midway through, or abandon melee once his resistances are below 50% and chain BURNDAYRAZ for the kill. The Crystal Ball seems likely to spawn, so take advantage of this and purchase this awesome boost to your Mana spike; if you get lucky, and see a Piercing Wand, you should have an even easier time finishing him (especially if you're a Gnome). Still, this dungeon will remain a bit of a hit-or-miss, because you will most likely need that little extra push from items appearing in the stores to beat the boss.
In any case, even before starting to worship The Earthmother, do not kill too many of the Mysterious Murkshades; remove only as many as you need to for moving around. Each plant will translate to a precious Mana point in the endgame, and you will most likely use up most (or all) of them during the boss fight.