I'll leave that for your thread, as it seems more like an "overhaul" than a conversion at this point.
This next one differs from the psionic dragon of the same name.
Obsidian Dragon
Created by: Mark Mathis
FREQUENCY: Very rare
NO. APPEARING: 1-2
ARMOR CLASS: -2
MOVE: 12”/30” (MC: B)
HIT DICE: 13-15
% IN LAIR: 65%
TREASURE TYPE: H, R, U (X2)
NO. OF ATTACKS: 2 claws, 1 bite, and 1 tail strike
DAMAGE/ATTACK: 2-8/2-8/6-48/2-16
SPECIAL ATTACKS: Major breath weapons, exceptional damage from bite, four attacks per round, major spell use
SPECIAL DEFENSES: Magic resistance, high intelligence, detects hidden/invisible objects, fear aura, savingthrow bonus with age, polymorph self at will, low armor class
MAGIC RESISTANCE: 5%
INTELLIGENCE: Exceptional
ALIGNMENT: Any lawful
SIZE: L (56' long)
PSIONIC ABILITY: Nil
CHANCE OF:
Speaking: 75%
Magic Use: 85%
Sleeping: 15%
LEVEL/XP VALUE: 13-14 HD: X/13,250 + 18 per hit point; 15 HD: X/17,550 + 20 per hit point
Obsidian dragons appear in most respects to be like silver dragons. The main difference between the two is that obsidian dragons are black with silver highlights. Known only from the northern reaches of the continent of Oerik (in the WORLD OF GREYHAWK® setting), obsidian dragons are thought to be distant but more powerful cousins of silver dragons, originating (some speculate) in the Land of Black Ice. All obsidian dragons are lawful. Some 65% are of good alignment, while 25% are neutral and 10% are evil. As with silver dragons, these creatures are able to polymorph themselves at will in order to appear to be a human or normal animal.
The obsidian dragon's tail attack only affects those targets within 20' of the tail itself. The breath weapon of the obsidian dragon is a cone of black acidic frost, 90' long with a 30' se. Creatures who fail their saving throws vs. dragon breath take the usual damage from cold, equal to the dragon' hit points, but they must save again at -2 to avoid taking 2-16 hp acid
damage as well (no acid damage is taken if this second save is made). This breath weapon can be used three times per day. Three times per day, the obsidian dragon can also breathe forth a membranous web of black ice 10' in diameter, shot up to 60' away. Those failing a saving throw vs. dragon breath are enveloped in the web and encased in 5-8" of black ice by the end of that round. All encased creatures are held immobile and must make a second saving throw vs. breath weapon to keep their faces from being covered. Otherwise, they will suffocate in 2-5 rounds unless they can make their bend bars/lift gates strength rolls to break free, or unless the black-ice web suffers at least 12 hp damage (attack vs. AC 4). One-quarter of the damage done to the blackice web is instead inflicted on the victim so
encased.
While very young, obsidian dragons are able to cast three first-level spells. At each age thereafter, they gain three more spells of one higher spell level, plus one spell from each lower spell level. Thus, an ancient dragon could cast 10 first-level spells, nine second-level spells, eight third-level spells, etc. Ancient dragons have a 25% chance of knowing one ninth-level spell. Furthermore, 45% of magic-using obsidian dragons have spell books, so they may select spells for use rather than knowing only a limited number of spells per level.
Obsidian dragons take -1 hp/HD of cold damage inflicted upon them. They are not immune to their own breath weapons. In addition, they take + 1 hp/HD of heat-, fire-, and electricity-based attacks.
Originally appeared in Dragon #146 (1989).