I think it would work better as an eternal as far as the entire 'mind-game' type thing goes. However, it would be an absurd benefit for the other player to not see your health or his for any lengthy amount of time.
I think so too, but i have trouble figuring out a simple, intuitive way to make it still useful when you have >=2 of them in hand.
Eternal spells are supposed to be playable an unlimited amount of times per turn (quanta permitting), right?
If not, i could modify that into 1 time per turn per card, but i'd need extra space to explain all that. I have this rule that if the required card text is longer than the Card Builder's allowed space, i consider it too complicated and cut out some features.
About your 2nd statement, assuming you mean "drawback" instead of "benefit" (else i don't know what you meant), that would be the whole point of the card's mechanic, because too short amounts of obscured time are unlikely to make the enemy make bad decisions. He could just do some quick maths and reach accurate estimations, essentially negating the effect of the card.
I'd like to make it increasingly difficult for the enemy to keep track of what's going on, the more Obscures you play. Kind of like how it becomes impossible to control someone's permanents/creatures the more PA/Quints he casts.
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Just saw the comments posted in the meantime. As far as i'm concerned, i do the maths every turn when playing Elements, it really helps achieving victory to know if you can wait X more turns before playing SoSac/Skyblitz, how many cards your opponent is able to play if you stop your Sundial/Dim Shield/SoSac chain, how big can i let this Lava Golem grow before i must antimatter it, and such things. It can take fair amounts of time in PvP, FG and Arena fights.
This card is aimed specifically at PvP, (unless the AI can pretend making mistakes
) and yeah it aims to make calculus too time-consuming or unaccurate to be worth it, among other things. I think it could bring some new interesting strategies to the metagame, by bringing this new form of control: there was QC, PC, CC, hand control, and Cloak was the only information control but limited to your field. This adds targeted information control over things you couldn't obscure before.