In Ancardia exist werewolves, wererats and vampires. As we all know (from descriptions in ADOM) there are former humans (I mean, sentient beings).

So. Why can't PC become, for example, a werewolf? Remember, for example, Elder Scrolls II Daggerfall. I do not mean creating a race of werewolves like in Slash'em.

Now, how I see it.

Werewolves.
Ability to shapeshift - free but forced at full moon, at will but for some PP in other nights (maybe disabled in daytime/new moon?), PC drop everything he wear except rings/neck/girdle, increased speed and battle abilities, but only weapon is fangs.
Increased regeneration and resistance to poison/sickness, protection from bleeding.
PC CAN be good, but CAN'T be lawful. So alignment in chaos-law drop to NC at least.
Significantly increased damage from silver and lawful creatures. Problems within cities - people dislike werewolves. And hunt them.

Wererats. ?
--------- see werewolves ---------
(As for me - I dislike it.)

Werecats. ?
^_^ Just imagine that PC becomes one of Cat Lord subjects.

Vampires.
Ability to drain HP, stats (your stats temporarily increased).
Better regeneration.
Protection from sickness, death rays.
Speed increased.
Hunger - you can eat only blood. And only by draining HP of warm-blooded creatures.
Problems with holy water and good/lawful altars.
Increased damage from good and lawful creatures. Takes some damage or decreased stats in wilderness.
Alignment only E-C or E-CN
Social problems - see werewolves.


Now, how PC becomes one? As for werecreatures - in fight with them, with VERY low probability, maybe when receiving critical damage or when bleeding. As for vampires - for example, when PC low of HP and vampire drains him. And again, with very low probability.

And at last,

Ring of Hircine - artifact ring, gives ability to shapeshift freely.

Other ideas?