This new dark spell will be available at town hall 10 (with the dark spell factory at level 4).
It's the "Invisibility spell". Any troops, aerial or terrestrial, will be unattainable by all defenses and traps as long as it remains in the circle. Its effect will be longer when the level increase.
I'd prefer a "Cloak" spell that doesn't make them invisible/untargetable, but rather reduces incoming dmg by say 15% for 10s.
That would be great for helping on infernos as it gives a means of damage reduction (since heals don't work) without just always bringing the ubiquitous freeze.