This is probably illegal, but I'm a rebel.
Werebat
Huge Shapechanger
HitDice: 4d8+12 (30 HP)
Initiative: +0; +6 (+2 Dex, +4 Improved Initiative)
Speed: 30 ft.; 20 ft., fly 40 ft. (average) as bat
AC: 10; 22 (-2 size, +2 Dex, +12 natural) as bat
Attacks: Unarmed Strike +0 melee; or bite +4 melee as bat
Damage: Unarmed Strike 1d3 subdual; bite 2d6+4 as bat
Face/Reach: 5 ft. by 5 ft./5 ft.; 15 ft. by 15 ft./10 ft. as bat
Special Attacks: Bat empathy; plus curse of lycanthropy as bat
Special Qualities: Sonar, damage reduction 15/silver as bat
Saves: Fort +9 Ref +6 Will +7
Abilities: Str 17, Dex 15, Con 17, Int 12, Wis 12, Cha 10
Skills: Listen +10*, Move Silently +7, Spot +10* as bat
Feats: Flyby Attack, Improved Initiative as bat
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Climate/Terrain: Temperate and warm desert, forest, hills, plains, and underground
Organization: Solitary
Challenge Rating: 4
Treasure: Standard
Alignment: Always Nuetral Evil
Advancement: By character class
In humanoid form, all of the sample lycanthropes have the following ability scores: Str 11, Dex 11, Con 11, Int 12, Wis 12, Cha 10. Their only skill is a Craft or Profession skill as +7, and they have Skill Focus in that skill as their one feat
Werebats in humanoid form tend to be dark-eyed, shy, and elusive. They have pug-noses and sharp teeth, and tend to avoid bright light and favor raw meat.
Combat
Werebats use their ability to fly to a maximum advantage, swooping down on unsuspecting prey and flying out of range
Sonar (Ex): Werebats emit high-frequency sounds, inaudable to most other creatures, that allow them to locate objects and creatures within 120 feet. Echolocation is as percise as sight, but does not revel color. It is effective even in darkness, fog, or similar conditions of low visibility. It reveals invisible creatures. A silence spell negates echolocation and forces the werebat to rely on it's weak vision, which has the maximum range of 10 feet in it's bat form.
Skills: *Werebats gain a +4 bonus to Spot and Listen checks while using sonar
In the Realms
Werebats are often found in the Underdark, and frequently come from drow stock. As such, they often have significantly better skills, ability scores, and class abilities then the simple commoner werebat described above.
Taken from pages 91 and 92 under the template appendix in "Dungeons and Dragons(R) Monster Compendium: Monsters of Faerun" (c) 2001, 2002 Wizards of the Coast, inc. Made in the USA. Please don't sue me.