Because a defense of 5 with an auto shield is really really sick.
STEALTH POUNCE
If Black Panther attacks a figure that did not have clear line of sight to him at the start of this turn, or if Black Panther was on a Shadow space at the start of this turn, add an
additional automatic skull to his attack.
The additional isn't needed at all. It is like trying to avoid redundancy with the first power by being redundant.
Also, right now I am not sure what to do right now if my Black Panther meets both requirements: on a shadow space and not visible to the defender before moving.