I feel like this would have a great flavor as a green card named something like "Constricting Coils," with the flavor of a snake squeezing harder every time someone tries to breath... but unfortunately, the ability isn't green.

And when I say "this," I just mean an ability similar to this. Maybe even on a snake.

I like this idea, but it seems to hurt you more than help you... unless your deck is chock full of instants, then it feels fine. That being the case, shouldn't it just target instants? I mean, unless this card is put in a set with a very large proportion of Flash permanents? Either that, or remove the word "you cast a spell" and replace it with "a spell is cast" taxing everyone for everything...

I guess I don't understand why this needs to be friends with flash and instants. If I cast a creature spell, and this is out, my opponent's creatures all cost more until my next turn... right? The same should be true of artifacts, sorceries, etc. I agree, it has the potential to hurt you some, but only if you want to cast four artifacts on your turn. It seems like it will hurt your opponents more. Am I not thinking about this correctly? Or did I get the wording wrong?

Oh, hmm, I misread it as "UEOT" rather than "until the beginning of your next upkeep". I'd guess jmg did as well.

Huh. I wonder if that would be a common issue.