Gulguthydra (CR 12)

Huge Aberration
Alignment: Usually neutral
Initiative: +0; Senses: darkvision 60 ft., Listen +8, and Spot +8

AC: 23 (-2 size, +15 natural), touch 8, flat-footed 23
Hit Dice: 15d8+105 (172 hp)
Fort +12, Ref +5, Will +10
Speed: 30 ft., swim 30 ft. (surface only)
Space: 15 ft./15 ft.
Base Attack +11; Grapple +18
Attack: 2 tentacles +14, 6 bites +12
Full Attack: 2 tentacles +14, 6 bites +12
Damage: Tentacles 1d6+5, bite 2d8+2
Special Attacks/Actions: Improved grab
Abilities: Str 20, Dex 10, Con 24, Int 6, Wis 9, Cha 15
Special Qualities: Nauseating stench
Feats: Cleave; Great Cleave; Improved Bull Rush; Iron Will; Multiattack; Power Attack
Skills: Listen +8 and Spot +8
Advancement: 16-30 HD (Huge); 31-45 HD (Gargantuan)
Climate/Terrain: Any forest, marsh, and underground
Organization: Solitary
Treasure/Possessions: None

Source: Monster Compendium: Monsters of Faerûn

Improved Grab (Ex): To use this ability, the gulguthydra must hit with a tentacle attack.

Nauseating Stench (Ex): Any corporeal being with 8 or fewer HD who comes within 80 feet of a gulguthydra must make a Fortitude saving throw (DC 23) or be nauseated for the next 1d10 rounds. At the end of the period of nausea, if still within 80 feet of the gulguthydra, the being must make another save. A single successful save exempts the being from needing to make saves against any gulguthydra's nauseating stench ability for one day. Nauseated beings are unable to attack, cast spells, concentrate on spells, or do anything else requiring attention. The only action a nauseated character can take is a single move (or move-equivalent) action.

Gulguthydras are not subtle. They move straight toward what looks most edible, grab it in their tentacles, bite it with their teeth, and eat it. Exposed skin, fur, or leather armor attracts the gulguthydra's attention. Food encased in metal armor is its second preference.