Steam Mephit

Fast healing works only when the mephit is in contact with warm or hot steam or boiling water.

As a standard action, the mephit can transform itself partially into warm steam. While in this form, the mephit always benefits from its fast healing and gains a 20% miss chance against attacks and effects targeting it directly. In addition, the mephit takes only half damage from area effects. Returning to its normal form requires a move action. The mephit can remain in this form for a number of rounds per day equal to 3 × its CR, but these rounds need not be consecutive.

caster level equal to CR, high attack bonus