User blog comment:Mich, Michele & Kuhla/Future Units Preview/@comment-26336535-20151229171542/@comment-27000255-20151231105959

Critical spark (not to be confused with criticals) are like criticals, have a chance to increase damage. Critical sparks are 1.5x more damage than normal spark but arent affected by buffs, for now.

Dont underestimate it, its literally double damage if you crit spark. (Very good for nuking, same for Marabelle in general.)