Hello, first post of me.
I don't have knowledge of DCSS programming, so I don't know how much coding this would take, or if this is possible at all with Dungeon Crawl code.
but anyway, here is my idea:
Vault of a RattenkönigChance of generation in each level, that contains rats.
Should contain many single rats and a
rare chance of a
Rattenkönig.
If a Rattenkönig is generated, it is composed out of a random number of rats (more rats, lesser chance, mix of different rat types possible).
Rattenkönigs are always confused, but each rat it contains has of course the chance for an attack in a combat round (with chance to desease).
In sewers there should even be the (very, very rare) chance of generation of a
Vault of The Rattenkaiser.
The Rattenkaiser is by default a big Rattenkönig which contains additionally a single 'leader rat' (the Kaiser), which has the abillity to try to chancel the confusion state each turn by chance, but also to fart Mephitic Cloud. If a Rattenkaiser is generated in a game, there is no chance of generation of a additional one, even if the first gets killed.
The Kaiser should always have the possibility to leave the Rattenkaiser and flee. The Rattenkaiser becomes a Rattenkönig in this case.
From wikipedia:
Rat kings are phenomena said to arise when a number of rats become intertwined at their tails, which become stuck together with blood, dirt, ice, excrement or simply knotted. The animals reputedly grow together while joined at the tails. The numbers of rats that are joined together can vary, but naturally rat kings formed from a larger number of rats are rarer. The phenomenon is particularly associated with Germany, where the majority of instances have been reported. Historically, there are various superstitions surrounding rat kings, and they were often seen as an extremely bad omen, particularly associated with plagues.
The original German term, Rattenkönig, was calqued into English as rat king, and into French as roi des rats. The term was not originally used in reference to actual rats, but for persons who lived off of others.
The phenomenon may have diminished when the brown rat (Rattus norvegicus) displaced the black rat (R. rattus) in the 18th century. Sightings have been sporadic in the modern era; most recently comes an Estonian farmer's discovery in the Võrumaa region[4] on January 16, 2005.
Specimens of purported rat kings are kept in some museums. The museum Mauritianum in Altenburg (Thuringia) shows the largest well-known mummified "rat king", which was found in 1828 in a miller's fireplace at Buchheim. It consists of 32 rats. Alcohol-preserved rat kings are shown in museums in Hamburg, Hamelin, Göttingen, and Stuttgart. A rat king found in 1930 in New Zealand, displayed in the Otago Museum in Dunedin, was composed of immature Rattus rattus whose tails were entangled by horse hair.[5] Relatively few rat kings have been discovered; depending on the source, the number of reported instances varies between 35 and 50 finds.
http://en.wikipedia.org/wiki/Rat_king_%28folklore%29