Yowch, okay, that was too close for comfort. Judging by the skill the Shield used, it was likely that it was resistant to thunder attacks. So before the smoke screen wears off, Frisk opts for an Ice Ninjitsu, reappearing for just a moment to fling giant ice shuriken at the shield. A moment passes, and they touch down behind it, now fully visible again.
same as last attack, but with ice damage instead of lightning