I could think of a few other unique traits to make werebats interesting and more unique?
- Aren't bats carrion eaters (omnivores in the broadest sense of the word)? Give them a corpsedevouring / regen ability much like the ghouls have?
- Give them a bonus to movement speed like werewolves / higher stealth skills to represent the "flight"?
(- Alternatively, give them a sort of additional temporary movement speed bonus while transformed into a bat?)
- The sound angle? Where most lycanthropes rely very strongly on smell to track instead. You could even take it so far as to give them a sort of additional ability, like the spell Umber Hulks use? Sonic based, causing a chance to confuse and deafen in a cone before them (limited use.) This would somewhat make up for their lacking combat statistics compared to the other lycanthrope templates (and flight being impossible to implement properly)?
In my eyes, werebats add plenty of a unique perspective, even without proper flight. The difference between them and wererats isn't insanely big, but still large. Bigger than that between all the "woodland-based lycans"? (Prefer the same meat, hunt and track the same, travel the same, make the same or similar sounds, prefering solitude or small groups, etc.) Perhaps the biggest difference would be in the question, would werebats consider forming uneasy alliances with the undead forces? Something every other lycanthrope almost immediatly answers with a resolute "NO.", but carrion eatering partners in crime might?