Brood Bat

Brood Spawn. The brood bat has advantage on saving throws against being charmed, and magic can’t put the brood spider to sleep.

Echolocation. The brood bat can't use its blindsight while deafened.

Keen Hearing. The brood bat has advantage on Wisdom (Perception) checks that rely on hearing.

Regeneration. The brood bat regains 10 hit points at the start of its turn if blood has been spilled this round. If the brood spider takes radiant damage or damage from holy water, this trait doesn't function at the start of the brood spider's next turn.

Sanguine Slip. As a bonus action, the brood bat can magically turn into bloodmist, teleporting to any space large enough to fit it. The space must be within line of sight.

Sunlight Sensitivity. While in sunlight, The brood bat has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one creature. Hit: 7 (1d10 + 2) piercing damage, and the target must make a DC 11 Constitution saving throw, taking 18 (4d8) poison damage on a failed save, or half as much damage on a successful one. If the poison damage reduces the target to 0 hit points, the target is stable but poisoned for 1 hour, even after regaining hit points, and is paralyzed while poisoned in this way.