Boss: Nine of the regular bosses (all but Bleaty, Firstborn and Medusa), plus Kinissssch (HP 475, ATK 90, Magic Resist 50%, Magical Attack, Corrosive, Death Protection (50))
A Hooded Figure will be somewhere in the map. Talk to them to take a one-way trip to the Arena.
The arena has 2 main areas: The Prayer Room and The Arena. The Prayer Room as a bunch of purchasable altars. They cost 20 gold each. The Pactmaker altar is free. '
The arena has three shops. They hold a keg of mana, a keg of health and The Amulet of Yendor. In each of the four corners a monster is spawned. One is level one, one is level four, one is level six, and one is level nine, and they are automatically bloodless.
In the Arena, you will face nine bosses in waves of three. The nine consist of Lord Gobb, Frank the Zombie, Tomithy Longdall, Super Meat Man, Jörmungadnr, Aequitas, The Iron Man, The Tormented One, and The Tower of Goo. After each wave the blackspace, monsters and bosses are replenished.
After you defeat the third wave, the blackspace is replenished and Kinisssch shows up on the battlefield.
Regen-fighting is the word here. Poison is useful, as are mid-battle level-ups using the corner enemies. The piece de résistance in the boss gauntlet is usually the Tower of Goo and its 75% physical resist: you'll need to either save a lot of mana for this battle, or bring a lot of resistance erosion to it.
Tikki Tribute - Level up fast with catapult tricks. Worship Tikki Tooki in the clean up phase to get poison, then convert to Mystera for the arena. Use poison to kill all of the bosses without special strategies and follow directions for the ones that do. Convert to the Glowing Guardian or Dracul for extra hp and/or mana after you run out of potions.
Orc Rogue/Glowing Guardian - Prepare Glowing Guardian, attack bonus increasers, Patches, and an item that either provides high attack bonus or high conversion rate. Buy and convert all possible items you won't use later (using bonus potions to get an early level catapult), use Absolution ~5 times for some bonus HP. The objective is to get base damage to achievement levels (150+); this makes poisonless regen-fighting a doable strategy.