Bat

A bat is a flying passive mob that spawns in dark areas. It is the only ambient mob in the game, intended to complement the game's atmospheric settings.[1]

Bats can spawn in groups of 8‌[JE only] or 2‌[BE only] in the Overworld at a light level of 3 or less at any y-level, on blocks of stone, granite, diorite, andesite, tuff, or deepslate that are not directly exposed to the sky. They also need at least 1.5 air blocks (with for instance, a top trapdoor or top slab in the block above foot level). In Java Edition, they can spawn in any Overworld biome except the deep dark. In Bedrock Edition, there are also other specific biomes they cannot spawn in.​[more information needed]

Bat entities do not count toward the passive mob cap, as they are considered ambient creatures in the entity inheritance, and therefore fall into the dedicated ambient category.