Level
4th
Casting Time
1 Action
Range/Area
60 ft.
Components
V, S, M *
Duration
2 Rounds
School
Transmutation
Attack/Save
None
Damage/Effect
You target one creature within range that you can see and whose Natural Armor is derived in part from its scales (a Pit Fiend or a Dragon, for example). The creature must make a CONS save versus the spell's DC. On success, the creature is unaffected. On a failed save, the creature's Armor Class is reduced by 5 and the target creature becomes vulnerable to all damage types for the next 2 combat rounds.
* - (a bit of pumice that is consumed in the casting)
I would increase it to all natural armor as scales is a purely flavorful element.
Edit:I suggest cleaning up the second half of the spell to be
"The target must make a constitution saving throw or their Armor Class is reduced by 5 and the target creature becomes vulnerable to all damage types for the next 2 rounds."