We need to double check that this is in fact the same monster, but there's a nupperibo in both the Tome of Horrors (plus ToH Revised) and the Fiendish Codex II. In that case, I don't think we should do a CC conversion. My understanding is that part of the deal creating the CC was not to convert monsters WotC did an official version of.
We're converting a "Maturing Baatorian" here, not a Nupperibo.
The scenario claims that the Nupperibo is only a "larval stage" of a Baatorian, and after many eons they metamorphose into the creature under discussion.
A Nupperibo is a mindless 3 HD dough-man who's barely smart enough to thump an enemy with a weapon.
This creature is intelligent, has double the HD, additional special defenses and has sprouted a collection of blood-draining tentacles.
Nupperibos being Baatorians contradicts the Nupperibo's official AD&D writeups (all 3 of them), which say they are merely damned souls who aren't wicked enough to become larva. I'd suggest this means only a few "Nupperibos" are actually Baatorians, and the rest are just Baatezu.
Here's an extract of the Planescape Appendix (1994) version of the Nupperibo, to show some of the differences:
BAATEZU, LEAST—NUPPERIBO
CLIMATE/TERRAIN: Baator
FREQUENCY: Common
ORGANIZATION: Army
ACTIVITY CYCLE: Any
DIET: None
INTELLIGENCE: Non- (0)
TREASURE: Nil
ALIGNMENT: Lawful evil
NO. APPEARING: 1–100
ARMOR CLASS: 9
MOVEMENT: 6
HIT DICE: 1
THAC0: 19
NO. OF ATTACKS: 2 or 1 (by weapon)
DAMAGE/ATTACK: 1d2/1d2 or by weapon
SPECIAL ATTACKS: Nil
SPECIAL DEFENSES: Regeneration
MAGIC RESISTANCE: Nil
SIZE: M (5 feet tall)
MORALE: See below
XP VALUE: 120
* SNIP *
Nupperibos are blind, deaf, and mute.
COMBAT: Nupperibos, like lemures, attack any nonbaatezu they encounter in Baator, heedless of their own safety. They need never check morale, for they fight until destroyed.
A nupperibo attacks with two claws (1d2 points of damage each). When they form armies, they receive weapons, though seldom anything better than a club. In these cases, they do damage as per weapon type.
They regenerate 1 hit point per round in Baator or any other lower plane. Any piece of a nupperibo, including its burnt ashes, regenerates. Only holy water, a holy sword, or other sanctified weapon can destroy one permanently.
The mindless nupperibos are immune to all mind-affecting spells such as
charm person or illusions. Of the special powers common to all baatezu, nupperibos use
cause fear, and that only under orders and when at least 10 nupperibo all attack the same defender.