This has the potential to be brutal against any deck that depends on creature abilities. Lobo can remove ONE skill for 4
upped, while this costs only 7
and wipes the whole field clean.
I don't know how to balance this card better, but it's a bit... hard to tell right now if it's even balanced as is. It won't remove Momentum, but it's a way to deal with the pesky quinty oty.
Personally, I see little point in upgrading this shield. There are TONS of good 1|X critters out there with abilities:
Parasite
Virus/Retrovirus
burrowed Antlion
Gnome Gemfinder
Lycanthrope/Werewolf
Red Nymph/Fire Nymph
Armagio
Amber Nymph/Gravity Nymph (!!)
Rustler/Leaf Dragon
Ray of Light
Guardian Angel
Deja Vu
Arctic Squid/Arctic Octopus
Nymph Queen/Water Nymph
That's substantial. Can Malignant Cell be lobotomized?