The überjackal effect or überjackal bug is a term used by many players to refer to a certain ADOM game mechanic, which causes some very common monsters like jackals to become considerably more powerful over the course of the game, occasionally killing players who are unprepared for it. The bug is said to have only appeared in v 1.1.1; it is due to be fixed in 1.2.0 (presumably by raising the KPL of some monsters commonly affected by this) .
Experience mechanic Edit
Similar to the PC, ADOM creatures can accumulate experience and attain higher level. In this process, they increase in DV, PV, to-hit, damage, hit points and speed, and so become overall more respectable opponents. The PC will witness this process when monsters fight each other, as monsters leveling up will yield the message "The [creature] suddenly looks more powerful!". The PC will also roughly recognize the amount of experience a creature has by "l"ooking at them.
As the PC grows stronger, monsters will tend to be created at higher levels, to prove a greater challenge, and yield more XP in return. This is usually a slight effect, and monster strength still greatly depends on the danger level of the current dungeon. In most cases, this effect is so small that a high-level PC will not notice the difference.
Another factor that leads to monster created at a higher level is the PC's number of kills of this monster - the more instances of a specific creature the PC has killed, the higher the level of newly generated instances of this particular creature (a concept referred to "kills per level" — or KPL).
The tendency of some creatures to be generated in very high numbers will lead to this creature type quickly increasing in power. For creatures such as rats or goblins, this effect is subdued heavily to the point that they won't become a danger during a normal game even if a high number of wererats is created; presumably the Creator has set a certain values for each creature that dictates how heavy the effect is. The "bug" that is commonly referred to is the fact that some creatures stand out among the others as both very, very common and possibly created in huge numbers, and have their value for gaining experience set rather high. The oversight is thought to have arisen from the fact that monsters such as jackals, spiders, ants and bees are rarely generated under "normal" circumstances, thus having low KPL; but can be encountered in huge masses by summoners or dungeon features. The eponymic jackal, for instance, can be summoned by jackelweres, which are quite common in dungeons and guaranteed in the pyramid, and appear in wilderness encounters (along with several jackalweres to make even more jackals). They tend to become stronger at a high rate the more often the PC is forced to exterminate them along with jackalweres, until they become a threat even to late-game PCs. Since XP gains are halved every 30 instances of a creature killed, these very powerful jackals will also give piddly XP.
This effect leads to strange anomalies; for instance, large jackals and greater chaos servants will often be a great deal weaker in combat than their more mundane cousins, simply because they are not created in large numbers.
What causes many players to name this oversight amongst the worst bugs in 1.1.1 is the possibility of a true "überjackal" to be created. This refers to a single monster of this type that is created at such an oddball high level that it is capable of dealing several hundred points of damage per turn, and cannot be recognized on sight (apart from the "extremely experienced" tag, which is only visible if the monster is already standing next to the PC). This has happened with jackals, but seems to be an even more common occurrence among breeding worms of any color, and will eventually happen with battle bunnies. These "über"-creatures will take out high level PCs practically out of nowhere.
While death is a common thing to occur in ADOM, the defining factor of late game deaths is that they are normally caused by stupidity on parts of the player, as late game ADOM is generally fair; the überjackal effect causes sudden deaths the player felt very powerless about.
Avoiding the überjackal effect Edit
The effect is best avoided by becoming aware of the monsters that may eventually become "über" and avoiding killing large numbers of them. Most players aware of the überjackal effect for instance flee jackal wilderness encounters whenever possible. Breeders like the white worm are either taken out as quickly as possible or locked in and evaded altogether. The battle bunny level is finished in the quickest way possible, by digging or teleporting. Levels with beehives may be avoided or the hives blocked by locked doors to avoid increasing the strength of giant bee warriors.