Bat
Bats are flying mammals (the only ones in the real world, in fact). Associated primarily with Black mana, Magic's bats tend to be fearsome and dangerous, a stark constrast to the harmless tiny insect-eating flyers from our world (although those do exist on the Multiverse, such as Dakmor Bat). More often than not they are associated with Vampires.
The first card to bear the creature type Bat was Vampire Bats in Legends.
Innistrad Bats
On Innistrad vampires can change into bats which have such clarity of hearing that simple sounds become symphonies. Stensia is pestered by undead Marrow Bats.
Mirrodin Bats
Grimclaw Bats patrolled the Mephidross. Once Mirrodin became Phyrexia, they were compleated.
Ravnican Bats
Bats in Ravnica are primarily associated with the Orzhov Syndicate. Unlike other bats, which are primarily Black, these bats, specially the Blind Hunters, are mostly equally White as well. They are used as assassins and messengers.
Ulgrothan Bats
Sengir Bats accompany the infamous Baron Sengir, the vampire lord who rules the Dark Barony from Castle Sengir.
Vampire Bats
The classical Vampire Bats are titanic flying creatures that may be used as steeds, for example by Kulrath Knights. They occur in Dominaria and Shadowmoor, as well in a few other planes.
Bat tokens
1/1 Black Bat Creature tokens with flying are produced by:
1/2 Black Bat Creature tokens with flying are produced by: