For the breath weapon, may I suggest this ?
Breath Weapon (Su): A mithral dragon has one type of breath weapon, a line of searing silver light. Creature who fail their save are blinded for 1d6 hours.
and may I suggest these as an "upgrade" ?
- Furthermore, the light can dispel any darkness spell or effect as a caster level equal the dragon's HD (or sorcerer caster level)
*Note: I'm not sure if in the 2e edition, darkness spells could be countered by light spells and vice-versa. So please excuse my ignorance on this one.
OR
- Furthermore, any creature susceptible to silver, like lycanthropes or creatures with silver damage reduction, takes an additional +2 points of damage per age category.
*Note: It's raw silver light. I doubt a lycanthrope could really survive this kind of attack.
Again, I'm only proposing something to suitably upgrade this dragon, not to change it completely.