Another "soft counter." Unlike Snakefoil, I don't know how good this one feels. However, I have several different options for it:
1. "Counter target instant or sorcery spell. Copy that spell twice. You may choose new targets for the copies."
2. "Counter target spell unless its controller lets you copy it twice. You may choose new targets for the copies." Note that this can copy permanent spells: is that wise and/or possible? I'm sure Riku avoided copying creature spells for a reason.
3. "Counter target spell unless its controller lets ~ deal 3 damage to him or her and 2 damage to each creature he or she controls." My least favorite option, but there it is.
Note that I do prefer Snakefoil to any of these.

I agree with you, I like "Mana Burst" (though I still prefer Snakefoil) and want to print it as is, but it's a bit like Odds from Odds // Ends but less powerful, so it probably wouldn't actually be very useful in play. And the other options seem reasonable, but none seem perfect.

I think copying a permanent spell works under the rules but has always been avoided because most players wouldn't know how it worked, and it would need a "clone" token which is a bit confusing. So I'd like to try that (it would certainly make the spell playable), but it probably wouldn't work in the end. Perhaps do a different color creature-only version "exile target creature unless..."?

Mana Burst is definitely just a throwaway title. Anyway, I guess I don't understand why it's less powerful than odds. Is it purely because Odds has the other option, being a split card?

Sorry, I read too quickly and forgot this said copy twice, that is an improvement over odds. But what I mean is, giving the opponent the choice is a definite downgrade, because a noticeable portion of the time, either the spell will be something where opp doesn't really mind if you counter it (if you counter a cheap utility spell, they're probably content that you're both out one card) or it'll be a spell you can't really benefit from copying (eg. search for something you don't have, win the game if..., etc) and in either case it would provide almost no benefit since your opponent can choose the less useful version.

I'm worried those cases will be too much of the time, so this won't be that useful, even though I'm excited to try to play it on something like Cruel Ultimatum :)

I may be wrong, it may be fine as is (it's good some of the time, and the effects are definitely comparable in the right circumstances), and if not I hope it could be tweaked because I definitely like it.

Sometimes it's important to design cards that look splashy and fun but aren't as powerful as certain people might think.

"it's" => "its" (sorry, it's just annoying me :D)

OMG I'M AN ENGLISH MAJOR I CAN'T BELIEVE I DID THAT.

People with horrible Facebook grammar are definitely influencing me.

Reminds me of Wild Ricochet. I love "copy it twice" (also seen on Echo Mage). Those two suggest this should probably be rare though. Which is OK, as it means we can have Snakefoil as an uncommon counterspell and this as a rare one :)

Fair enough. The version I put on the card is my favorite. Is it everyone else's, as well?