Phantom Fungus (CR 3)

Medium Plant
Alignment: Always neutral
Initiative: +0; Senses: low-light vision, Listen +4, and Spot +4

AC: 14 (+4 natural), touch 10, flat-footed 14
Hit Dice: 2d8+6 (15 hp)
Fort +6, Ref +0, Will +0
Speed: 20 ft.
Space: 5 ft./5 ft.
Base Attack +1; Grapple +3
Attack: Bite +3 melee
Full Attack: Bite +3 melee
Damage: Bite 1d6+3
Special Attacks/Actions: -
Abilities: Str 14, Dex 10, Con 16, Int 2, Wis 11, Cha 9
Special Qualities: Plant, greater invisibility
Feats: Alertness
Skills: Listen +4, Move Silently +5, and Spot +4
Advancement: 3-4 HD (Medium-size); 5-6 HD (Large)
Climate/Terrain: Any underground
Organization: Solitary
Treasure: None

Source: Monster Manual

This ambulatory fungus is naturally invisible, making it a feared predator among subterranean inhabitants.

A phantom fungus looks like a brown and greenish-brown mass though it is visible only when dead. A cluster of nodules atop the main mass serve as sensory organs. The creature feeds and attacks with a gaping maw lined with rows of calcitic teeth. Four stumpy legs support the creature and allow it to move about.