They have 2 more HD, deal 1 die greater damage, have 3 points better AC, move a tad bit slower, and have a pain attack rather than disease breath.
The bite of a kala (make a normal attack roll) inflicts no damage, but it injects a terrible toxin. The venom causes progressive pain unless the victim makes a successful saving throw vs. poison. These pains begin slowly and build in intensity. On the first round of effect, the victim notices discomfort similar to a strong headache. On the second round, the pain spreads, causing the victim to suffer a -1 penalty on his attack and damage rolls, and a +1 penalty on all saving throw rolls. By round three, the pain is quite strong, increasing the penalties to -2/ +2. By round four, the pain is excruciating, and the penalties are -4/ +4. By round five, the pain is so great that it incapacites the victim; he cannot move, attack, or take any other actions. From the time of the initial bite, the pains last for 1-3 turns.
We figured out the pain effect, but not its delivery. It has a bite that deals no damage. Should we model it off the vampire, requiring a grapple? Or simply add a secondary bite attack that deals only "pain"?