Help scaling a faerie dragon from CR 6 to CR 3

So I have a player who wants a Faerie dragon familiar and she has taken the improved familiar feat. The Draconomicon stats out a Faerie Dragon at CR6. I would like some help scaling it back to a CR 3 (I am terrible at this).

I am thinking change HD from 8d12 to 4d8
and scaling back the Spell like abilities as follows:
Keep:At will - dancing lights, detect magic, ghost sound DC 13;
3/day - glitterdust DC 15, obscuring mist
Change - 3/day - invisibility to self only
Lose - 3/day - charm monster DC17; entangle DC14; major image DC 16
- 1/day - animate objects, mind fog DC 18; project image DC 20; summon
nature's ally IV
-1/month commune with nature

Change caster level from 12th to ??? 5th or 6th

Any suggestions or opinions would be greatly appreciated. Thanks

HD function sort of funny with familiars.

I'd just use a half-dragon Grig - it is already CR 3 and has appropriate abilities, more or less.

Stuart

Yeah, HD function funny with familiars, as do skills and saves.

In general, the familiar uses it's master HD or it's own, whichever's better (but always has half the master's max HP as the familiar's max HP); uses it's master's base saves or it's own, whichever's better; uses it's mater's skill ranks or it's own, whichever's better; and so on. Racial HD change the base saves and familiar's own skill points. They effectively get Weapon Finess for free ("Attacks: Use the master’s base attack bonus, as calculated from all his classes. Use the familiar’s Dexterity or Strength modifier, whichever is greater, to get the familiar’s melee attack bonus with natural weapons. Damage equals that of a normal creature of the familiar’s kind.")

Gets kinda wierd when you go for non-standard familiars.