Way of the Open Fist
This challenge is set in Ick Swamp, and as such is infested with plants. As the monk depends on regenfighting, the goal then becomes to manage plant clearing with avoiding crippling debuffs.
The boss's Weakening Strike ability encourages switching to finishing, and the guaranteed Earthmother altar supports that with Clearance and Greenblood.
Preps: Whatever scroll you like, Can of WHUPAZ, Burn Salve, Fortitude Tonic, Health Potion. Races: Depends on whether you want to have an easier time with the boss, or getting to the boss. Orc and Human work well to clear the level, but the tools to kill the boss with a sustained fireball damage fight are there, so Gnome would also work well.
Do standard Monk regenfighting stuff as much as you can. Before you level up, clear out all the visible mana burn and poison plants in the way. Prey on high-level Gorgons, Vampires, and Meat Men. Wait to worship Earthmother until you're ready to fight the boss, as it becomes very difficult to move around when you can't clear away plants. For the boss, you can use a Greenblood strategy to get a bunch of free corrosion damage on the boss, or you can use a Clearance strategy to fireball the boss down.
Platemail works well here, comboing with the Monk's natural damage reduction and Vineform if you're feeling saucy to massively reduce damage done. Unfortunately, it does leave you vulnerable to Nagas, who would normally serve fairly well as popcorn. Obviously, the monk loves damage items, and if you go Gnome, a Trisword can translate into a bunch of extra damage on the boss. If you go the fireball boss kill route, standard caster items like Crystal Ball and Battlemage Ring are good finds. Viper Ward and Soul Orb give you a great deal of freedom to clear plants, and give a great deal of CP when you're done clearing plants. While it is not an item, HALPMEH is very good here as well, allowing you to clear poison plants with impunity, as well as playing into the Monk's attrition strategy by offering more health/tile explored.