I like it! Simple, straightforward, and balanced.
^ I agree.
My only critique is that the unupped may be slightly too strong compared with AM...
Upgraded AM costs 6
and reverses attack (e.g. a change of -200%), this costs 1
and gives a change of -50%
I.e. 6/200 = 3 / 100 ; 1 / 50 = 2 / 100... so this is about 50% more efficient at reducing damage advantage per turn.
The unupgraded actually matches exactly with unupgraded AM damage advantage cost efficiency.
This is probably only a minor balance issue though, so it may not be hugely important to fix.
Other than that I like this card alot.
Good Job!