How to bring the pet to the valley of dead

One thing that is very important in hell is fire resistance. The fire traps in Gehennom are particularly nasty because, unlike normal fire traps, they decrease your maximum HP unless you're resistant. You should also fireproof your armor (by reading a scroll of enchant armor while confused for example) and put all items that could burn or boil into a bag, so they won't be damaged or destroyed.

As to the level drainers: The best defense against level drain attacks is magic cancellation. If you have an item which offers level 3 magic cancellation, this will cause drain attacks to fail in most cases, making level drainers much more harmless.

For fighters it's also a good idea to have a silver saber as those are especially effective against demons and the undead (well, most undead - zombies don't care, but zombies aren't really dangerous at this stage anyway).

Also note that you can eat wraith corpses to gain levels.

General things you should do before you enter the end game:

• Get your naked AC down to 2 or lower with divine protection (you can get it down to 0 quite easily via donations).

• Have magic resistance and reflection.

• Be fast (or preferably very fast)

• Make sure all of your stats (except charisma) are close to or at their maximum

• Enchant most of your armor to +4 or +5.

• If you're a fighter, enchant your weapon to +6 or +7.

• If you're a caster make sure that all your important spells are recent in your memory or you have the spellbook in your bag of holding. You do not want to forget magic missile while battling The Wizard or Death.

• Make sure you have a means to detect portals (not important in Hell, but once you leave the dungeons, that's gonna come in handy and you do not want to have to go searching for gold detection scrolls after you have woken The Wizard).

• You should also have a reliable way to cure sickness (blessed unicorn horn or cure sickness spell) as there will be a couple of enemies who can make you terminally ill.

The penalty for killing it is actually pretty small, only one point. Which is regained easily by killing normal monsters. I would not bother to much thinking about it.

Funny detail, killing a peaceful has a -1 alignment penalty. Killing a hobbit has a +6 alignment bonus. So net you gain points. With a big if. You only get the bonus if the hobbit is hostile. So you first need to make the hobbit hostile and not kill it in one hit.

Murdering peaceful humans does have a large penalty. You lose two points of luck and telepathy. Unless you are chaotic, which has no penalty.

If you are doing it for moral reasons, tricking the game into killing it is still breaking your moral code. Bad hacker! No ascension for you.

If this doesn't bother you, you might try using pets, or Traps. Magic doesn't work (and does not give a warning). Perhaps polymorph system shock might work. But not sure on that.