Yeenoghu

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Yeenoghu, &, is a monster in NetHack, and one of the demon lords.

Generation

Yeenoghu is generated with a flail.

Yeenoghu, together with Juiblex, is one of the two demon lords that can be summoned with own-race sacrifice. If the player is lawful or neutral when performing this type of sacrifice, the demon princes will be hostile when summoned; if the player is chaotic, they will be peaceful. There is also a 1260 chance that a water demon may gate in Yeenoghu or Juiblex. So it's possible for him to appear quite early in the game and obliterate a weak character.

Strategy

Yeenoghu can deal out tremendous physical damage if you lack free action and MC3; his melee attacks can also gate in other major demons, and he can zap you with magic missiles as well, meaning he is immune to them and death rays on top of his high monster magic resistance. However, Yeenoghu he is not generally regarded a problem if you are prepared for him.

Like other demon princes, Yeenoghu is covetous will teleport next to you to deliver melee attacks and fire magic missiles. When at low health, he will teleport to the upstair tile to regenerate, and will escape up them if approached too closely; the usual strategies for covetous monsters apply, including obstructing the upstair or else luring him to a floor with a blocked upstair. As he is able to summon Demogorgon directly, dispatching him quickly is advised.

Yeenoghu respects Elbereth; however, as of NetHack 3.6.1, Elbereth does not work in Gehennom, where Yeenoghu is most likely to be encountered. Keep this in mind in the event he is found outside Gehennom (e.g. via water demon or a non-Gehennom bones) and you have a character capable of surviving his onslaught. However, the chances of having such a character in this scenario is often several degrees lower, and you may be better off escaping and avoiding the floor entirely if somehow possible. Even if you can take the fight to him, remember that in 3.6.0 and later versions you cannot attack him while on an Elbereth, either; on top of this, Yeenoghu's confusing gaze will complicate your attempts to engrave, and his tendency to teleport after you at the first opportunity usually means little time to prepare beforehand unless you can lure him to a pre-engraved Elbereth elsewhere.

History

Yeenoghu first appears in NetHack 3.0.0.

"A ludicrous bug"

Yeenoghu is the subject of one of the longest-running bugs in NetHack history. In NetHack 3.1.0, the Riders were introduced. The code that handles their special attacks comes right after that which handles Yeenoghu's confusion attack.[1] Early versions had this code inserted carelessly; consequently, after Yeenoghu used his confusion attack, execution would proceed into the section that handles Death's touch:[2]

Yeenoghu reaches out with its deadly touch.--More--
Do you want your possessions identified? [yn]

A comment at the end of Yeenoghu's section read:

/* fall through to next case */

and contemporary source-divers thought from this that the behavior was deliberate. Thus for many years the bug was never reported.

Pat Rankin of the DevTeam was made aware of this property in a rec.games.roguelike.nethack discussion, and called it "a ludicrous bug".[3] The then-current version was NetHack 3.3.1. In NetHack 3.4.0, Yeenoghu's illicit deadly touch was taken away.

Umber hulks were not affected, because their confusion attack is handled in a different part of the code.[4]

These source excerpts might make clear the origin of the bug. Here is src/mhitu.c lines 999-1012 from NetHack 3.0.0, which was before the Riders existed:

#ifdef HARD /* a non-gaze AD_CONF exists only for one of the demons */
            case AD_CONF:
                hitmsg(mtmp,mattk->aatyp);
                if(!mtmp->mcan && !rn2(4) && !mtmp->mspec_used) {
                    mtmp->mspec_used += (dmg + rn2(6));
                    if(Confusion)
                         You("are getting even more confused.");
                    else You("are getting confused.");
                    make_confused(HConfusion + dmg, FALSE);
                }
#endif
                /* fall through to next case */
            default:    dmg = 0;
                        break;

Here is a partial quote of src/mhitu.c lines 1214-1258 from NetHack 3.1.0, the first version to implement the Riders:

            case AD_CONF:
                hitmsg(mtmp, mattk);
                if(!mtmp->mcan && !rn2(4) && !mtmp->mspec_used) {
                    mtmp->mspec_used = mtmp->mspec_used + (dmg + rn2(6));
                    if(Confusion)
                         You("are getting even more confused.");
                    else You("are getting confused.");
                    make_confused(HConfusion + dmg, FALSE);
                }
                /* fall through to next case */
            case AD_DETH:
                pline("%s reaches out with its deadly touch.", Monnam(mtmp));
                [... the rest of the Rider code ...]
            default:    dmg = 0;
                        break;

The Rider code was carelessly placed between the AD_CONF section, which handles Yeenoghu's confusion attack, and the default section, where it was supposed to finish. Thus execution improperly proceeded into Death's touch attack.

The bug was written up as bug C331-96[5] and was fixed in NetHack 3.4.0. Here is src/mhitu.c lines 1474-1486 from NetHack 3.4.3:

            case AD_CONF:
                hitmsg(mtmp, mattk);
                if(!mtmp->mcan && !rn2(4) && !mtmp->mspec_used) {
                    mtmp->mspec_used = mtmp->mspec_used + (dmg + rn2(6));
                    if(Confusion)
                         You("are getting even more confused.");
                    else You("are getting confused.");
                    make_confused(HConfusion + dmg, FALSE);
                }
                dmg = 0;
                break;
            case AD_DETH:
                pline("%s reaches out with its deadly touch.", Monnam(mtmp));
                [... the rest of the Rider code ...]

The "dmg = 0;" and "break;" lines duplicate the ones in the default section, and Yeenoghu is restored to his pre-3.1.0 behavior.

Variants

In UnNetHack, Yeenoghu no longer respects Elbereth.

In Slash'EM Extended, in honor of the "ludicrous bug", Yeenoghu gets the extra ability to zap the player with finger of death. Unlike the touch of death, however, reflection can save the player here.

Origin

Yeenoghu is drawn from Dungeons & Dragons. He is the demon lord of gnolls, which resemble anthropomorphic hyenas. In that depiction, he wields a triple flail.

Encyclopedia entry

Yeenoghu, the demon lord of gnolls, still exists although
all his followers have been wiped off the face of the earth.
He casts magic projectiles at those close to him, and a mere
gaze into his piercing eyes may hopelessly confuse the
battle-weary adventurer.

References