a big "B" on the map that I saw in the jungle the other day:

a huge swarm of bats, darkening the sky
It is a huge swarm of bats, consisting of tens, if not hundreds, of thousands
of bats. The swarm darkens the sky and the noise of flapping bat wings is
awesome. Occasionally some guano falls on you, eww. A single bat is not very
big or dangerous, but this amount of bats is extremely dangerous if agitated.
It is in excellent shape.

The sound of thousands of flying bats is deafening.

Monster lore, from Jkk:
You concentrate and ask 'haven't I seen you before?'
A huge swarm of bats, darkening the sky
Bat neuter
Offense grade: 159.932%
Assuming it hits with every attack, it would inflict wounds of godlike
destruction.
Defense grade: 119.163%
It has awe-inspiring protection against swords and axes.
It has awe-inspiring protection against spears and arrows.
It has awe-inspiring protection against clubs and hammers.
It has awe-inspiring protection against claw and bite attacks.
It reacts strangely to damage.'
This creature laughs off injuries that would kill any normal person.