If it's upside-down, the rules turn it into a colorless, nameless, typeless, 2/2 creature with no abilities.

Then the rules would need to be changed so that Lurk works, wouldn't they?

I'm not sure a repeatable on-board counter spell would be printed with that cost. Most of them involve sacrifice, several put some restriction on the type of spell that can be countered, and many are soft counters. The closest I could find was Ertai, Wizard Adept, whose ability costs more, and he's legendary.

I admit, I will not like the day when this becomes an activated ability on an efficient creature. This is a lot of mana, though, and while it may not require the discard or have the restrictions of a card like, let's say Stronghold Biologist, It should be happening in a stage of the game where the control player has already won. At this point, it might as well be Meloku The Clouded Mirror. The game should be over.

I would be a little more concerned with Zombify however. While I know the activation cost will stop this card from being spectacular, free Cancels are nothing to sneeze at.

­Ertai, Wizard Adept and Ertai, the Corrupted have activated countering on tap. Like those, this does only get one spell per turn. (Unless blue has any untap effects... oh wait.) And I'm not sure you can really call a 3/4 for an "efficient" creature. That kind of creature gets Ancestral Recall as a tap ability, if you remember Arcanis the Omnipotent...