Quoting Kongdej, reply 4
You are right... EXCEPT I had all my 8 mana blast cancelled when the enemy countered 1 of them, so something is amiss....
After now being able to use it 4 or 5 times, every unit has resisted for me as well, not sure if that is just bad luck though.
Resisted? I was talking about 9 stopped mana blasts out from 1 counter-spell, not resisting, just being canceled.
Have a pretty late-game save lying around for random testing