Size & Type: Small Magical Beast (Psionic)
Space/Reach: 5'/5'
HD: 3, 4 (Medium), 7 (Large)
Speed: 40', Fly 70' (Average)
Ability Scores: Str -4, Dex +6, Con +6, Int -4, Wis +0, Cha -4 - Net +0, three penalties
Natural Armor: 5
Natural Weapons: Two Primary Claws (1d4), one Secondary Bite (1d6), one secondary Gore (1d6)
Skill List: Hide, Listen, Spot
Body Shape: Winged Humanoid-ish
Speech (Languages): Yes (Common, Terran)
CR: 4
WotC LA: -
Our LA: __

There's also an aquatic version that uses their wings to propel themselves through water at their fly speed. It's not clear if they can still fly or suffer any other downside for this, but feel free to assume this is strictly better if only in a niche way. I doubt adding a swim speed is going to be the straw that bumps this up a level.

Similarly to their stone cousins, Crystal Gargoyles have no need to eat or breathe, and can hold perfectly still (requiring a DC20 Spot check to notice they're alive). These are also immune to cold, have DR 15/magic (whcih is actually still relevant at this level), and Weapon Finesse as a bonus feat. They get a +4 racial bonus to Hide checks when concealed against stone, and a +10 bonus when concealed in water or against ice.

You have Charm Person and Inflict Pain as once/day PLAs, at ML3. You also have the once/day SLA to unleash a burst of light from your crystal body, treated as a CL3 Color Spray, but in a 40' radius burst instead of a 15' cone. Unfortunately, the save DC is based on your penalized Charisma. Still potentially handy though.