For the CR, I'm using Upper_Krust's simple rule (version 5) that advancing a mindless ooze increases the CR by 0.45 each HD.
Fully Advanced Bone Ooze CR 39
Genderless Bone Ooze Advanced +40 HD
Neutral Colossal Ooze
, Senses ; ; Blindsight 60 ft.
AC 2, touch -13, flat-footed 2 (+5 natural, -8 size, -5 dex)
hp 1295 (HD); DR 30/epic
Immune mind-affecting effects, gaze attacks, visual effects, illusions, poison, sleep effects, paralysis, polymorph, stunning, critical hits, flanking; SR 72
Spd 30 ft.
Melee Slam/ ( Strength Drain Dexterity Drain Constitution Drain +5 Wounding)
Base Atk +45;
Space 30 ft. ft.; Reach 15 ft.
Atk Options Engulf, Bone Meld
Special Actions Heals 5 HP every time it drains abilities, 10 on a critical hit; excess as temp HP
Abilities, , , Int — ,
Skills Hide -21
Bone Meld (Ex): Any creature a Bone Ooze has engulfed must make a DC 60 strength check or die. After 1d3 rounds, all equipment and flesh is discarded from inside the ooze, leaving the skeleton inside.
Engulf (Ex): A Bone Ooze can simply roll over a gargantuan or smaller creature, and effects as many opponents as the ooze can cover. Opponents can make a DC 60 reflex save to get out of the way (moving back or to the side on a success), or they can forego this save and make an attack of opportunity (and be engulfed even if they hit). The Bone Ooze cannot engulf and make a slam attack in the same round. Each creature engulfed is considered grappled and trapped inside the ooze's body. Engulfed creatures take automatic slam, ability drain, and wounding damage every round it remains engulfed.
Wounding (Ex): A creature hurt by the Bone Ooze starts bleading uncontrollably until the bleeding is stopped with a DC 15 heal check or any cure/healing spell. Each round, a bleeding creature takes 5 more points of damage then they took from bleeding last round. e.g., the creature takes 5 damage the first round, 10 points the 2nd, 15 points the 3rd, and so on.