A hound of ill omen appears to the offender out of a ghostly haze, and howls once. In that howl, the target creature is instantly made aware of the transgression that they are being punished for. All within 120 feet can hear the howling, but only the chosen target(s) of the god's wrath can see the creature. After howling, the hound turns and pads back into the mist, disappearing.
The creature bearing the curse of ill omen feels a sense of dread and impending doom. No healing magic functions on the creature. The next time they take damage, they take quadruple damage. This happens a total of 1d10 times before the curse is lifted. The cursed creature isn't necessarily aware of the nature of the curse (until they take damage), or how many hits are required to lift it. Self-inflicted or intentional damage doesn't count against the 1d10 instances of damage -- only injuries the creature seeks to avoid will count.
Removing the curse is impossible by normal means. A remove curse spell used by a priest of at least 12th level within one turn of the howling will reduce the number of wounds by half (1d10, divide by two, round up), but this is the only known mitigating factor.
The hound can be slain (and it is not more powerful than any other common dog), though only those who can see the hound can strike it. If slain, the god is instantly aware of the slaying, each creature involved in the slaying, If the slayers were not the target of the original curse, they now become targets of the curse. If the original target of the curse is among the slayers, the effects of the curse are doubled, and no magic can reduce its severity. There's also a 70% chance that the offended deity will send another servant (such as a deva or an aasimon) to punish the transgressor further.
It is said that each god has one (and only one) hound of ill omen. Slain hounds reform on their deity's plane in 1d4 days. No other deity will interfere with the sending of a hound of ill omen.
Monstrous Compendium Annual, Volume 3