KILLamari DOOMacy

So I swiped The Wisdom Frog Croaks' guy's DM notebook. He's been doing this Nintendo/Ravenloft mash-up called "Barovania" and I wanted to see what he had in store. This is an excerpt for a high level adventure called "Descent Into The Murder-Pits Of The Dark Prince" which strikes me as a liiitle on the nose, but hey, whatever.

Statue of the Dark Prince, located in room 3B

DUNGEON LEVEL 3
ROOM 16
The hallways from rooms 4, 5, and 8 all open into a large oval chamber, some 500' feet from end to end, and about 200' feet from side to side. The room is shaped like a bowl, and the ground is absolutely covered in dusty, ancient bones and pieces of long rusted armor and weapons. Around the perimeter of the room, some 15' above the ground, are audience seating (room 31). The walls to climb out are smooth and subject anyone attempting it to a -15% chance to climb. However, before anyone tries to climb out, they will have to deal with the trio of deadly necromantic constructs left in this room by the Dark Prince.
The Killamari Doomacy are spherical piles of human and demihuman bones, roughly two foot in diameter, and held together by the necromantic rituals of the Dark Prince. They move by rolling, and are tasked with smashing anyone who enters the chamber. They always moves their full distance each round unless somehow restrainted, and makes a single attack on any target they passes through, on up to three targets per turn. Further, if it is allowed to move the full 15', then it will pull many of the bones on the floor with it, increasing its size and increasing its HD by 1, until it has reached its full potential  of 12 HD.

Close up of the Killamari

Killamari Doomacy
Frequency: Very Rare
No. Appearing: 1-4
Armor Class: 3
Move: 15"
Hit Dice: 2
No. Attacks: Up to 3
Damage/Attack: Special (1-4 at start)
Special Attacks: None
Special Defense: Immune to cold and spells that influence the mind
Magic Resistance: None
Intelligence: None
Alignment: None
Size: S (2' diameter) up to L (12' diameter)

The Killamari attacks by rolling over people. The base damage is d4, but for every 2 HD it gains, it increases its damage by one die size (d4 becomes d6, d6 becomes d8 etc) until it reaches its maximum damage capability of dealing 1-20 damage at 12 HD. Furthermore, once the damage dice reaches d10, each attack has a chance of knocking the victim over (They must roll under their dexterity OR constitution, whichever is higher, to remain standing). However, the Killamari's AC actually increases by one point each time it increase in size, as it provides an easier target to hit.