I'm fighting Ryth in Infinity Blade 2. When I do combos, most of the time I can hit that guy with hits where he loses about 120 health — the text then reads "Combo Hit".
But sometimes, my laser blade being equipped with an ice gem — I manage a "Combo Ice" and then Ryth loses 4000+ health points.
How is it determined when a Combo Ice, or more generally, a Combo Element, happens? Is it pure chance?