With the Season 2 Update the Backlash trait got reworked, the below has been taken from the Season 2 Patchnotes:
As Backlash is a Trait that currently only feature the Firestaff I suggest to add an Frost Orb related effect.
Backlash (Frost Orb Effect)
Frost Form causes attackers to suffer Frost damage (equivalent to Fire-shield Block) and buildup.
