What if this spell lasted only the turn it was played, a temporary bonus that your enemy would not experience.
This would be a hell of a spell with a army of malignant cells and the enemy without titanium shield/jade shield/diamond shield though, even if it did just last one turn. Even with the enemy having titanium/jade, a full compliment of malignant cell with "lethal" would do alot of damage in one turn for the quantum used.
You could rename it predatory surge (surge, since it lasts only one turn) The upgrade could cost less, but still only provide +1 and have the same name.