Groovy. Well, let me go ahead and post the half-red-dragon ruster I was initially considering:
Lare Dragon (Advanced)
Hit Dice: 10d10 +36 (95 hp)
Initiative: +2
Speed: 40 ft, fly 80 ft. (average)
AC: 22 (-1 Size, +2 Dex, +11 natural), touch 11, flat-footed 20
BAB/Grapple: +10/+22
Attack: Antennae touch +18 melee (rust)
Full Attack Antennae touch +18 melee (rust) and 2 Claws +13 (1d6+4) and bite +13 (1d8 + 4)
Space/Reach: 10 ft. / 10 ft.
Special Attacks: Rust, Breath Weapon
Special Qualities: Darkvision, low-light vision, scent, Immunity to sleep and paralysis, Fire immunity
Saves: Fort +11, Ref +9, Will +8
Abilities: Str 28, Dex 15, Con 19, Int 4, Wis 13, Cha 10
Skills: Listen +13, Spot +13, Survival +6
Feats: Alertness, Track, Flyby Attack, Hover
Environment: Underground
Organization: Solitary, Pair
Challenge Rating: 8
Treasure: None
Alignment: Always Neutral
Advancement:10-15 HD (Large)
COMBAT
A rust monster can scent a metal object from up to 90 feet away. When it detects one, it dashes toward the source and attempts to strike it with its antennae. The creature is relentless, chasing characters over long distances if they still possess intact metal objects but usually ceasing its attacks to devour a freshly rusted meal.
The creature targets the largest metal object available, striking first at armor, then at shields and smaller items. It prefers ferrous metals (steel or iron) over precious metals (such as gold or silver) but will devour the latter if given the opportunity.
Rust (Ex): A rust monster that makes a successful touch attack with its antennae causes the target metal to corrode, falling to pieces and becoming useless immediately. The touch can destroy up to a 10-foot cube of metal instantly. Magic armor and weapons, and other magic items made of metal, must succeed on a DC 23 Reflex save or be dissolved. The save DC is Constitution-based and includes a +4 racial bonus.
A metal weapon that deals damage to a rust monster corrodes immediately. Wooden, stone, and other nonmetallic weapons are unaffected.
Breath Weapon: Once per day a half-red-dragon can breathe a cone of fire that deals 6d8 points of damage. A successful DC 17 Reflex save reduces damage by half