Just your run-of-a-mill bat.
Bat (CR 1/2)
N Tiny Animal (Avian)
Init +2; Senses Blindsense 20 ft., low-light vision; Perception +6
AC 14, touch 14; flat-footed 12 (+2 Dex, +2 size)
hp 5  (1d8+1)
Fort +0, Ref +4, Will +2
Speed 5 ft., Fly 40 ft. (good)
Melee Bite +4 (1d4-2)
Space 2.5 ft.; Reach 1 ft.
Special Attacks Critical Attack, Screech
Str 6, Dex 15, Con 6, Int 2, Wis 14, Cha 5
Base Atk +0; CMB -2; CMD 8
Feats Toughness*, Weapon Finesse
Skills Fly +15, Perception +6; Racial Modifiers Perception +4
Critical Attack (Ex)
Once per day as a standard action, the bat can inflict more pain than normal. If they succeed at hitting with their bite attack, the damage is 1d4-2 x 1.5 for total damage.
The master of a bat familiar gains a +3 bonus on Fly checks.
Once per day as a standard action, a bat can produce an ear-splitting screech that stuns non-bats in a 20-foot-radius burst. All creatures within the area must make a DC 12 Fortitude save or be staggered for 1d2 rounds. Other bats are immune to this effect. This is a sonic mind-affecting effect. The save DC is Wisdom-based.