Caustic Creeper (CR 4)

Medium Magical Beast
Alignment: Always Lawful Evil
Initiative: +3 (+3 Dex)
Languages: understands Draconic

AC: 18 (+3 Dex, +5 natural), touch 13, flat-footed 15
Hit Dice: 6d10 (33 hp)
Fort +7, Ref +8, Will +3
Speed: 50 ft.
Space: 5 ft./5 ft.
Base Attack +6; Grapple +8
Attack: bite +8
Damage: Bite 1d8+3
Special Attacks/Actions: Acidic Wounds
Abilities: Str 14, Dex 16, Con 14, Int 6, Wis 12, Cha 10
Special Qualities: Immunity to acid, fear, sleep, paralysis. Trackless
Feats: Improved Natural Attack (bite), Power Attack, Track
Skills: Hide +7, Move Silently +6, and Survival +3
Advancement: 7-12 HD (Medium); 13-18 HD (Large)
Climate/Terrain: Temperate or tropical forests.
Organization: Solitary or with master (Green dragon)
Treasure/Possessions: None

Source: Dragon #357

Bully (Ex): Vicious and brutal killers, caustic creepers take an especial delight when facing fearful opponents. They gain a +1 morale bonus on attack and damage rolls against shaken opponents. This bonus increases to +2 versus frightened opponents and +4 against panicked opponents.

Acidic Wounds (Ex): Whenever a caustic creeper is wounded with a slashing or piercing melee weapon it releases a spray of acid. A creature that makes such an attack with a melee or natural weapon must succeed at a DC 15 Reflex save or take 1d6 points of acid damage. This save DC is Constitution-based.

Trackless (Su): A caustic creeper moves without leaving a trail, as per a druid's trackless step ability.

Skills Caustic creepers have a +8 racial bonus on Hide and Move Silently checks made in forests and similar terrain. They also gain a +4 racial bonus on Survival checks when using scent to track.