User blog comment:Crimson Storm Mich/Future Units Preview v2/@comment-30462510-20170629035104/@comment-26514197-20170630023351

It's basicaly those red sparks but with a slightly stronger boost.

Crit and Elemental vulnerability are fairly new but a few other units (Maxwell, Griff, Velma, etc) already have one or both of these buffs. They're not very good IMO.