This is an absolute wrecking ball in casual. I keep ranting about this "you need to be prepared"...but with this thing, how do you possibly prepare for THIS?!? Only thing you can do to stop it is countermagic, and that is all.
When pressured, blue mages can pay 6 mana for a counterspell. I've seen them pay four and five, even in tourney environments. Six ain't gonna be too much more of a crunch, especially when its the toolbox Istunbul just explained it was.
It is the ultimate counterspell to anything. Combos? Attacks? Upkeeps? Damage? ANYTHING? Just drop Time Stop and go on with your safe butt. This is a hideous mockery of the game. Six mana is far too low. Personally, I woulda treated this more along the lines of Fist of Krosa or Future Sight, and cost this sucker at 3UUUU. Force it hardcore blue, which is hard in casual, and pump up that price by one more mana.