I actually think maybe the effects should be reversed.
I imagine the big use of this would be creature control. Your opponent has too many creatures or creatures that are too strong, so you want to blast them. If I were to use it on a field full of fire flies/queens, I would rather the opponent get 1/1 creatures that I can block with skull shield, rather than 2/2 creatures that I cannot.
It would be nice to use with poisons like this, as well, since, if you can lower the damage from both player's creatures, poison can do a lot of damage.
Just my two cents, elite skeletons on the unupped, and normal skeletons on the upped would seem better.