None in particular. I imagine it's a bit of blend of flesh jelly and darktentacles (replacing tentacles with other body parts).
Sounds OK. Shall we take a darktentacles, increase the size to Gargantuan and turn it into an 24 HD Undead?
Somewhat ironically, the 3rd edition
Monster Manual II darktentacles has slam attacks rather than tentacles, which I think is fine for the "Undead Mass".
That would give something like:
Undead Mass
Gargantuan Undead
Hit Dice: 24d12 (156 hp)
Initiative: +1
Speed: 30 ft. (6 squares), climb 20 ft.
Armor Class: 21 (-4 size, +1 Dex, +14 natural), touch 7, flat-footed 20
Base Attack/Grapple: +12/+36
Attack: Slam +20 melee (1d6+12) or battleaxe +20 melee (2d6+12/×3)
Full Attack: 24 slams +20 melee (1d6+12); or battleaxe +20/+15/+10 melee (2d6+12/×3) and 23 battleaxes +20 melee (2d6+6)
Space/Reach: 20 ft./15 ft
Special Attacks: Constrict 1d6+12
?, enhanced multiweapon fighting, improved grab
?
Special Qualities: All-around vision, blindsense 60 ft., darkvision 60 ft., undead traits
Saves: Fort +8, Ref +9, Will +14
?
Abilities: Str 35, Dex 13, Con —, Int
?, Wis
?, Cha
?
Skills: ?
Feats: 9
Environment: ?
Organization: ?
Challenge Rating: ?
Treasure: ?
Alignment: Always neutral evil
Advancement: 25-35 HD (Gargantuan); 36-72 HD (Colossal)
Level Adjustment: —
Description.
Flavour Text.
Proficient in all simple or martial melee weapons?
Cannot speak but understands X?
Combat
When making a full attack, an undead mass has 1 attack per racial Hit Dice it possesses.
An undead mass can make up to three attacks at once against a Small or Medium-size opponent. Against a larger foe, it can make three additional attacks for each extra 5 feet of face the opponent has, provided it has the reach. Against a Tiny or smaller opponent, the creature can make only one attack at a time. It can make a maximum of three attacks against all foes in any single 5-foot by 5-foot area.
Constrict (Ex):
Enhanced Multiweapon Fighting (Ex): Can wield weapons in all its limbs simultaneously without attack penalty, within some size limit (up to Large-sized light or 1-handed weapons?).
Improved Grab (Ex): Maybe give it a racial bonus to grapple, and/or that "hold opponent at -10 instead of -20" ability?