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/Possessions: None

Source: Monster Manual

Phantom fungi usually roam quietly, hunting for prey. They attack lone individuals almost anywhere, but when tackling groups they prefer open spaces where they are not readily evident.

Improved Invisibility (Su): This ability is constant, allowing the phantom fungus to remain invisible even when attacking. This works just like improved invisibility cast by a 12th-level sorcerer, and lasts as long as the phantom fungus is alive. This ability is not subject to the visibility purge spell. Once killed, a phantom fungus becomes visible after 1 minute.

Skills: Phantom fungus has a +5 racial bonus to Move Silently checks.