BAT

Many varieties are included in the category of ordinary bats. They will attack only if cornered and forced to. If startled, bats tend to become frightened and confused and will swarm around and fly into things, putting out torches, confusing spell casting, etc., if humans are concerned. Bat sonar allows flight in total darkness. Under fine flying conditions, a bat's armor class rating rises from 8 to 4. In certain large caverns there could be as many as 1000 or more bats.

Giant Bat. These creatures - giant versions of the carnivorous variety of the ordinary bat, with bodies 3' long and a wingspan of 5'-6' - dwell in dark caverns, usually underground. In flight they emit a high-pitched whistling sound, a navigational device which compensates for their poor eyesight.

Giant bats are highly maneuverable in flight—anyone with a Dexterity of less than 13 who fires a missile at a flying giant bat does so at -3 hit probability. For purposes of aerial combat, they are maneuverability class C.

The creature must land - usually on its victim - to attack with its bite (1-2 or 1-4 points of damage). 1% of victims bitten by giant bats contract rabies.

Only 10% of giant bats are of the 1 hit die variety.

Swarm. If startled, tiny common bats tend to become frightened and confused and will swarm around and fly into things, putting out torches, foiling spell casting, etc. (The GM will determine the exact effects based on the number of bats. Typically, a 20 ft. diameter area and a round or two after being startled with creatures in that area taking 1d4 or at most 2d4 damage to all in the area as the bats relocate.)

The huge mobat is found only rarely, and typically in warm climates where large caverns offer shelter and food is plentiful. They are omnivorous but prefer warm-blooded prey which they bite to death with their fangs. Mobats have a wingspread of 12-16 feet and so must have a large area in which to take off. Once airborne, however, their sonics allow them to fly through narrow places, even in total darkness. 

Their flight being rapid and fairly silent, they surprise prey 50% of the time.

They can also give a piercing screech which will cause such pain to prey that the victims seek to cover their ears rather than fight, unless a saving throw vs. paralysis is successful. The mobat's screech is always used if prey resists. The effective sound radius is 20 feet. 

Note that mobile mobats have an armor class of 2, and their reflexes and sonics enable them to dodge attacks. Under crowded flying conditions armor class 7 prevails. Out of the air, mobats are armor class 10. 

These monsters have a dim, evil intelligence and a desire for shiny objects.