Here are the conditions:

Human Cleric (best single class character in the game)
Max stats and HP at start

Restriction:
May not use most items. Only allowed starting holy symbol, starting rations (will be OK thanks to Create Food), magically created weapons (like Spiritual Hammers), the Grappling Hook (so that I can enable pits and make Detect Pits useful) and clerical scrolls. (The last one I'll probably never use, but it gives me something to pick up.) The rest of starting equipment will be dropped.

I may allow myself to pick up, but not use, the special equipment set the game decides to give me.

Dungeon/Game Environment settings:
18 floors
Minimum monster frequency (curious if this affects spawn rate)
Maximum monster difficulty
Lowest amount of treasure and rations
Food consumed slowly (Create Food makes this setting moot anyway)
No keys (so I don't have to worry about picking them up)
Water level enabled
Undead enabled (maybe Turn Undead will be useful?)
Enemy spellcasting enabled
Magic power at maximum

Working so far (though I did accidentally eat an apple).

One floor had Cockatrice (petrifies) and Spectres (drains levels and spells). That was not fun (though I encountered each ailment only once each and I'm not playing Death Real). It's a good thing Spiritual Hammers are ranged.

Of note:

Coins are common regardless of settings.
The Grappling Hook seems to be guaranteed to appear on the first floor.
I don't recommend playing with illusionary walls at the default frequency; they already appear a bit too much, which is annoying before you get True Seeing.
Low food consumption has one advantage: On floors with level draining undead, you don't need Create Food and Water and can prepare an extra Negative Plane Protection.
My rules make Magical Vestment useful (it isn't under normal circumstances), but note that it does not even stack with Dexterity bonus to AC.
With minimum monster frequency, the floors start out relatively empty, but enemy spawn rates don't seem to otherwise change. This leads to a nice difficulty curve on each floor; the floor starts out gentle, but by the end you are fighting multiple monsters at once.

9th floor: Hags (look like they cast spells, but don't) and Death Knights (look like they don't cast spells, but do).

I am playing with Enemy Spellcasting On and Spell Power at maximum. As one could see, that is a deadly combination.

The Death Knights' fireballs are *really* deadly, enough to take me from 84 HP down to 0 in one blast. Ouch!

It's a good thing I have the Protection from Fire spell, which doesn't seem to wear off after being hit with multiple fireballs.

I gained 2 levels on the floor, from 11 to 13. (Or maybe it was 3: Don't remember the level I started the floor on.) Those enemies fortunately give a lot of experience.

Teleporter maze, so sometimes I would end up in the midst of enemies.

Next floor: one of the enemies can hit for as much as 36 damage. That's not good, especially when my restrictions give me an AC of 3 (that's *with* Magical Vestment active). I should reach level 14 soon, which should let me get AC 2 with that spell.

At one point while fighting near a teleporter and accidentally going into it, I noticed there were 3 Spiritual Hammers in existence. While examining them, the game crashed. (Likely some memory corruption bug here; probably related to pointers in C.)

Edit: One more thing: The first time I was killed by a fireball, I didn't show up on the high score list (bug?) so I didn't know what killed me. The second time, it showed up as "killed by magic".

10th floor:
Enemies are Greater Faeyrs and Undead Beasts
Fireball traps exist on this floor. Protection from Fire blocks them, and they aren't too dangerous otherwise.
Have to heal constantly.

I am spontaneously gaining experience just by existing on this floor. (Enemies spontaneously killed by fireball traps? Or maybe they fail to spawn with positive HP?) In any case, I earned enough experience on this floor to go from 13th level to 18th level. Those extra casts of Heal will help.

Boss was a mummy, which did not survive Turn Undead. (That just shows how overleveled my character is now.)

Nice to see you playing this one.

As you know from other topics, I'm just starting my D&D crpging. I began my first run on Dungeon Hack last night. Unfortunately it was at like 1am and I had to be at work at 8 this morning. Rushing home tonight to go find floor #2. :)

EDIT: Running a half-elf fighter/cleric named, of course, Elvish Costello.

11th floor:

Every enemy on the floor (including the boss, as far as I can tell) is a Minatour.

Easy floor, but I only gained 1 level and only at the end of the floor.

Next floor is a teleporter maze with undead beasts. (Don't know what the other enemy is.) Of note, I can turn them, but not destroy them while turning.

This is the one good thing about thieves, their experience table is the most forgiving of any class (except bard, which is the same.) The cleric table isn't as bad as wizards, though. (The wizardly combination of frailty and a steep climb for levels is particularly unkind in a solo adventure.)

I actually see that as more of a downside; it makes thieves cap out sooner in dungeons that yield high XP (especially long dungeons with high monster difficulty). What's important is not level, but things like hit points and THAC0. For instance, if we assume 2.2 million experience and HP rolls just below average:

Thief (level 20): 50 HP, 11 THAC0. Is incapable of advancing any further.

Cleric (level 17, almost 18)): 54 HP, 10 THAC0. Is capable of advancing further, eventually reaching 60 HP and 8 THAC0.

As for wizards, all you need to make the game easy (especially if you are playing a dungeon without undead) is the Vampiric Touch spell. If you are lucky enough to find a scroll of that spell, learn it and use it to attack whenever possible; since the "temporary" HP stacks and doesn't wear off, you will find that it is very difficult to die from HP damage, and in my experience, other forms of death are surprisingly rare on the deeper floors. Unfortunately, you don't learn mage spells from level up, so that setup is too dependent on the RNG for my tastes. (Maybe I'll do a mage or cleric/mage run where I allow myself to hack one spell per spell level.)

The nice thing about Clerics is that they are self-sufficient; clerics and fighter/clerics do not have to rely on finding decent items in the dungeon to be effective, unlike everyone else. They don't even need to worry about finding rations after reaching cleric level 5!

Yeah, their max abilities are lesser, but they get there faster. I think you're right, though, I don't think there's a single point along thief progression where they fight even as well as a cleric with equal experience, so it barely helps. No friends to facilitate backstabs (or tank, for that matter) is a serious problem for solo thieves.

Actually, at low levels, thieves can fight as good or better than clerics, if we go by THAC0.

At levels 1 and 2, everyone has THAC0 20 (so, if we assume the weapon proficiency rules are not in use, mages can hit as often as fighters). At level 3, thieves get THAC0 19 while clerics are stuck at 20. Thieves catch up when they reach level 5 and pull ahead at level 7 (40,000 xp), becoming better at fighting until a cleric reaches level 7 (55,000 xp).

On the other hand, note that clerics get better hp growth and armor, and they also have the huge advantage of spell casting.

Floor 12: Same as floor 10, but with teleporters (but no traps) and the enemies don't spontaneously die. Was rather rough, but I reached level 20 mid-floor. Undead Beasts are annowing as they take reduced damage from weapon attacks and seem to be immune to fire damage, making fights with them very painful. Having all those casts of Heal definitely helped.

Floor 13 appears to have a spellcasting enemy (watchghost, I think). This should be interesting, but it means having to cast Resist Cold. In my test run, Fire Storm worked.

I have 102 HP, which is 10 less than the maximum possible for my class/level/constitution combination.