Ok, I beat the game on my third or fourth attempt. Here's a guide for how to beat it (don't read if you don't want any help!):
* The key is to get the mob to move next to you, so you can strike it on your turn
* To do this you will often have to sacrifice a turn, for instance by using inventory objects
* Save interactibles in a room to use for turn-skipping (pots, bookshelves, etc). Only interact with these immediately if you direly need a power-up, otherwise you'd better clear the surroundings of mobs first.
* Wells, anvils, book stand etc only skip a turn if you have the correct inventory.
* Levelling up will replenish your health; try to time this with an almost drained health not to waste power-ups
* Vials can be used right away, they increase the max health so no point in saving (unless for, again, turn skipping).
* Identify the traps, and lure your mobs to walk into them. This does not skip a turn btw.
* For mid-levels, save a cursed food item to use with an untampered weapon to upgrade the weapon on an anvil.
* The most annoying mob throughout the game is the red, teleporting mob. It will hit you and then fly away a short distance. This means that without turn-skipping objects, it can hit you repeatedly. If you have no turn-skipping objects handy, lure it into a tight space or a space with untriggered traps.
* The Eyes will shoot a confusion beam upon line of sight. Approach it diagonally. If you can't get right in turn, lure it into a safe room, preferably a tight space where you may attack it by chance.
* The toughest normal mob is the large ogre. He will hit you for 3 and has 20 h.p, which means until the last level he'll probably hit you at least twice.
* I think the scimitar is the hardest-hitting weapon. A Holy Scimitar on lvl 9 (your xp lvl, not the map level) hits for 20, and can one-shot even the ogre. There's no point in using other upgrades for weapons unless in the window where you can't one-shot the Ogre, but you'll still comfortably one-shot other mobs; in this case you may want to have a Basilisk-weapon ready. This has a chance to stun all mobs and you might beat the Ogre in two strikes with no counterstriking on his part.
* Carrot, bread, soup, steak (might have missed one) all heal double the HP with Holy as a prefix. Holy Steaks should be saved until level 8, if possible.
* Identify a mysterious weapon before using it; it might become stuck to you so that you can't discard it if it turns out to be cursed.
* Save some 10 HP or so before engaging with the Lich King, which is a mob somewhere on map level 8.