This was the Boss for a one-night adventure. Just to clarify, she is an Ogre with the lycanthrope template, who turns into a dire bat. She was originally the mate to the Ogre Half-Red Dragon (CR 5) recorded elsewhere on this site. I would surround her with some dire bats and swarms of regular bats for a brood; this also gives her some reinforcements or helpers to make the scene more interesting.
She can smell foes and has blindsight, so the darker she can get her lair the better. There may be a wind channeled through the lair that blows out torches and lanterns. She may just use swarms of bats to create the darkness and fight inside of that. She relies on her damage reduction as an edge in combat, so foes that can hurt her will be singled out. Since she appears as a giant bat-like creature, players may not initially know what the hell she is. This should add a little excitement to the encounter.
She does not have hover and her movement is good, so she will fly up to and attack one foe at a time, using a claw and Power Attack. Only after all silver weapons and casters have been dealt with would she choose to enter melee with a full attack, when she can keep range with flight. She is cunning, but not intelligent, and should have an escape route if her prey seems too much for her.
Groups without a paladin could be in trouble if afflicted by lycanthropy. They may need to withdraw from the dungeon and seek a cleric with remove disease.
Ogre Dire Werebat (hybrid form): CR 6; Large Giant (shapechanger); Init +5; Spd 40, fly 40 ft (good); AC 22 (natural +7, dex +5, size –1), touch 15, flat-footed 17; HD 4d8+11 plus 4d8+20; hp 67; BAB +6; Grap +18; Atk +12 claw (1d6+8); Full Atk two +12 claws (1d6+8) and +7 bite (1d8+4); Space/Reach 10 ft./10 ft.; SA Curse of lycanthropy; SQ Alternate form, blindsense 40 ft, damage reduction 10/silver, darkvision 60 ft, low-light vision, lycanthropic empathy, scent; AL CE; SV Fort +13, Ref +10, Will +8; Str 27, Dex 20, Con 21, Int 6, Wis 12, Cha 7.
Skills & Feats: Climb +8, Hide +7, Listen +9, Move Silently +7, Spot +9; Alertness, Iron Will, Power Attack, Stealthy, Toughness.
Alternate Form: The werebat can shift into animal form as if using polymorph, though its gear is not affected and it does not regain hit points when it changes form. Changing form is a standard action.
Blindsense: Characters targeted by blindsense still have total concealment unless the werebat can see them.
Curse of Lycanthropy (Su): Victims of the werebat’s bite must succeed at a Fort save (DC 15) or contract lycanthropy.
Possessions: potion of jump