Boomer

Deafening Boom. When a creature hits the boomer with a melee attack, the boomer releases a blast of sound. Each creature within 10 feet of the boomer that can hear it must make a DC 12 Constitution saving throw. On a failure, a creature takes 5 (2d4) thunder damage and is incapacitated until the end of its next turn. On a success, a creature takes half the damage and isn't incapacitated.

Death Burst. When it dies, the boomer explodes in a cacophonous burst. Each creature within 30 feet of the boomer that can hear it must make a DC 12 Constitution saving throw. On a failure, a creature takes 7 (2d6) thunder damage and is deafened for 1 minute. On a success, a creature takes half the damage and isn't deafened.

False Appearance. While the boomer remains motionless, it is indistinguishable from an ordinary fungus.

Shriek. If bright light or a creature is within 30 feet of the boomer, it emits a shriek audible within 300 feet of it. The boomer continues to shriek until the disturbance moves out of range and for 1d4 of the boomer's turns afterward.