Werecreature (or lycanthrope) is the collective name for wererats (@ / r), werejackals (@ / d), and werewolves (@ / d), a group of monsters which change back and forth between animal and human form. While in animal form, they can bite you which has a chance of conferring lycanthropy (indicated by the message "You feel feverish.") Lycanthropy is the name for the condition that makes monsters change form. You will become the same kind of creature as the one that infected you (ie. If infected by a werejackal, you will become a werejackal). Additionally, eating a werecreature's corpse will always infect you .
Werecreatures can summon their brethren for help (rats, jackals and any type of wolf, respectively). This will give the message "The werecreature summons help!", or "You feel hemmed in." if you cannot see any of the new monsters. If you are a werecreature, you can do the same with the #monster extended command. The summoned monsters appear as pets and will remain tame if your lycanthropy is cured.
You may hear the message "You hear a jackal howling at the moon" or "You hear a wolf howling at the moon". If so, a were jackal or werewolf is on the dungeon level somewhere.
If you chat to a creature (while blind or hallucinating, for example) and it mumbles inaudibly, so that all you hear is "moon", then it may be werewolf.
Werecreatures are particularly vulnerable to attacks made with silver weapons. It is a good idea to keep some on you at all times.
Most of the time, lycanthropy is unwanted, so don't engage in melee combat unless you have an effective way of removing the affliction. It makes your character unable to carry any kind of load, wield weapons, use hand operated things (such as open doors), and wear armor. While in animal form, your HP is generally considerably lower, as are many of your other attributes.
To remove the affliction, one may pray (the effectiveness of which is dependent on the usual factors), eat a sprig of wolfsbane, or quaff holy water. Before curing yourself, you may want to summon help (#monster), as having multiple pets can be helpful at certain times in the game, especially if you can improve them with a polytrap. Keep in mind, however, than having many pets can be burdensome too, as pets require food and will eat the corpses of animals that you wanted to eat. Pets may kill creatures that you had intended on keeping alive for the purpose of eating later or using in some other way.
When a werecreature summons help, 1d5 monsters of the appropriate type are created about the werecreature. The monsters will be created with the probabilities in the following table
And the SLASH'EM specific werecreatures
In SLASH'EM, Lycanthrope is a playable race, starting with (not hungerless) regeneration and lycanthropy (always a werewolf) which cannot be removed, but can eventually be controlled. They may only be chaotic. Also, any silver weapons in one's starting inventory (such as with Undead Slayers) will be reverted to their non-silver counterpart. See Lycanthrope (starting race)
Additionally, there are several new lycanthrope monsters in SLASH'EM: werepanthers, weretigers, werespiders, and weresnakes.
A werecreature summoning help in SLASH'EM will generate 1d2 monsters, rather than the 1d5 in vanilla.
In 1573, the Parliament of Dole published a decree, permitting
the inhabitants of the Franche-Comte to pursue and kill a
were-wolf or loup-garou, which infested that province,
"notwithstanding the existing laws concerning the chase."
The people were empowered to "assemble with javelins,
halberds, pikes, arquebuses and clubs, to hunt and pursue the
said were-wolf in all places where they could find it, and to
take, burn, and kill it, without incurring any fine or other
penalty." The hunt seems to have been successful, if we may
judge from the fact that the same tribunal in the following
year condemned to be burned a man named Giles Garnier, who
ran on all fours in the forest and fields and devoured little
children, "even on Friday." The poor lycanthrope, it appears,
had as slight respect for ecclesiastical feasts as the French
pig, which was not restrained by any feeling of piety from
eating infants on a fast day.
In the NetHack 3.0.0 days, lycanthropes in their animal forms were called ratweres, jackalweres, and wolfweres.