Werebat

Medium Humanoid lawful evil

Armor Class: 13 (in humanoid form, 14 (natural armor) in bat or hybrid form)
Hit Points: 66 (12d8+12)
Speed: fly 50 ft. walk 30 ft.
Challenge Rating: 3 (700 XP)
Source: Creature Codex, page 258

STR	DEX	CON	INT	WIS	CHA
12 (+1)	16 (+3)	12 (+1)	10 (+0)	12 (+1)	9 (-1)

Skills: perception +3, stealth +5
Damage Immunities: bludgeoning, piercing, and slashing from nonmagical attacks not made with silver
Senses: blindsight 60 ft., passive Perception 13
Languages: Common (can't speak in bat form)

Echolocation: The werebat can't use its blindsight while deafened.
Keen Hearing: The werebat has advantage on Wisdom (Perception) checks that rely on hearing.
Shapechanger: The werebat can use its action to polymorph into a bat-humanoid hybrid or into a Medium-sized bat, or back into its true form, which is humanoid. Its statistics, other than its AC, are the same in each form with the exception that only its true and bat forms retain its flying speed. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.
Sunlight Sensitivity: While in sunlight, the werebat has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

Multiattack (Humanoid or Hybrid Form Only): In humanoid form, the werebat makes two mace attacks. In hybrid form, it makes two attacks: one with its bite and one with its claws or mace.
Bite (Bat or Hybrid Form Only): Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 7 (2d4 + 2) piercing damage. If the target is a humanoid, it must succeed on a DC 14 Constitution saving throw or be cursed with werebat lycanthropy.
Claws (Hybrid Form Only): Melee Weapon Attack: +4 to hit, reach 5 ft., one creature. Hit: 5 (1d6 + 2) slashing damage.
Mace (Humanoid Form Only): Melee Weapon Attack: +4 to hit, reach 5 ft., one creature. Hit: 5 (1d6 + 2) bludgeoning damage.