Shrieker (CR 1)

Medium Plant
Alignment: Always neutral
Initiative: -5 (Dex); Senses: low-light vision

AC: 8 (-5 Dex, +3 natural), touch 5, flat-footed 8
Hit Dice: 2d8+2 (11 hp)
Fort +4, Ref -, Will -4
Speed: 0 ft.
Space: 5 ft./0 ft.
Base Attack +1; Grapple -4
Attack: -
Full Attack: -
Damage: -
Special Attacks/Actions: Shriek
Abilities: Str -, Dex -, Con 13, Int -, Wis 2, Cha 1
Special Qualities: Plant
Feats: -
Skills: -
Advancement: 3 HD (Medium-size)
Climate/Terrain: Any underground
Organization: Solitary, patch (2-4), or mixed patch (2-4 violet fungi and 3-5 shriekers)
Treasure/Possessions: None

Source: Monster Manual

Shriek (Ex): Movement or a light source within 10 feet of a shrieker causes the fungus to emit a piercing sound that lasts for 1d3 rounds. The sound attracts nearby creatures that are disposed to investigate it. Some creatures that live near shriekers learn that the fungus's noise means there is food nearby.

A shrieker has no means of attack. Instead, it lures prey to its vicinity by emitting a piercing loud noise (hence its name).

Shriekers and violet fungi often work together to attract and kill prey. When the shriekers' hellish racket attracts a curious creature, the violet fungus tries to kill it. Both enjoy the fruits of a successful hunt.