Should this be "Wheneven a player activates a creature's activated ability", as on Burning-Tree Shaman? Using "If" implies that this is wanting to be a replacement effect, but I'm not sure that's what you want.
I think emblems are almost a red-herring: "for the rest of the game" effects can usually be written with or without them; but you still want the effects to be mythic enough you don't forget, and I think this is fine.
OTOH, it doesn't really need to be "for the rest of the game": the other effects with that are riders on something else, but this could be an enchantment with hexproof and have 95% of the same effect (or an enchantment, and have 90% of the same effect). I also note that I'd probably rather have "gain 10 life" than "double my life total" on a one-off effect: the second is a lot more fun, but the first is what you need when you really need it.
It's certainly not a problem for the rules. There's a different issue on whether it's a problematic design due to memory issues.
There is some degree of precedent on "for the rest of the game" effects that aren't tied to emblems. See Stigma Lasher and Praetor's Counsel. So this is probably OK.
In theory, exiling the spell helps with memory issues, since then you wouldn't have to hide the card in your graveyard. Epic didn't do that... but that might be because it was pretty damn obvious that that was going to be the only spell that mattered from now on...
The Epic spells (Endless Swarm et al) didn't really have an issue. These days that sort of effect is tied to an emblem, but that's only been used on planeswalkers thus far.
Looking at gatherer, it seems red gets a 1R 2/1 upside, but haste is too big an upside (at least at common -- goblin guide shows they push that a lot at rare). I like this, but agree it probably needs to be tweaked.
Interesting comparison. Personally, I'd say that a 2/1 with a solid ability is a better card than a 2/2. Or, to put this another way, how many common 2cc 2/1s with a relevant keyword ability can you name that isn't white or green? Is there a 2/1 Shroud in Blue? 2/1 First Striker in red? (Black does get a 2/1 Lifelink... but they're clearly gearing black up to be the number 3 color in efficient beaters. One look at the new zombie grizzly bear gives that away.)
It's possible that this is fair, especially considering that the power level of creatures in Magic has increased over the years. I'm much more certain that this is powerful.
I'm trying to figure out at about how far up the pick list I would draft this card... assuming the occasional artifact, but nothing too relevant. In Mirrodin, this would be first pick material... but Siluras isn't Mirrodin. If this was Magic 2012, let's say? Maybe 2-3rd pick? But that set is very fast, and a 2/1 with Haste would go a long way there. If this was Rise of the Eldarazi, however, I might shelf this card to 8-9th pick, because I'd expect it to be trumped.
Quite a lot better than Hearth Kami, though that wasn't exactly pushing the power level. Still, I feel like it shouldn't have haste; compare with Ronom Unicorn / Kami of Ancient Law.
Should this be "Wheneven a player activates a creature's activated ability", as on Burning-Tree Shaman? Using "If" implies that this is wanting to be a replacement effect, but I'm not sure that's what you want.
Changed the restriction.
Shortend the text to be Hexproof rather then spelling it out.
I think emblems are almost a red-herring: "for the rest of the game" effects can usually be written with or without them; but you still want the effects to be mythic enough you don't forget, and I think this is fine.
OTOH, it doesn't really need to be "for the rest of the game": the other effects with that are riders on something else, but this could be an enchantment with hexproof and have 95% of the same effect (or an enchantment, and have 90% of the same effect). I also note that I'd probably rather have "gain 10 life" than "double my life total" on a one-off effect: the second is a lot more fun, but the first is what you need when you really need it.
Also, you could now template this as "Players have hexproof for the rest of the game" :)
It's certainly not a problem for the rules. There's a different issue on whether it's a problematic design due to memory issues.
There is some degree of precedent on "for the rest of the game" effects that aren't tied to emblems. See Stigma Lasher and Praetor's Counsel. So this is probably OK.
In theory, exiling the spell helps with memory issues, since then you wouldn't have to hide the card in your graveyard. Epic didn't do that... but that might be because it was pretty damn obvious that that was going to be the only spell that mattered from now on...
The Epic spells (Endless Swarm et al) didn't really have an issue. These days that sort of effect is tied to an emblem, but that's only been used on planeswalkers thus far.
Wouldn't there be some sort of rules problem with a sorcery having an effect for the rest of the game?
Looking at gatherer, it seems red gets a 1R 2/1 upside, but haste is too big an upside (at least at common -- goblin guide shows they push that a lot at rare). I like this, but agree it probably needs to be tweaked.
Interesting comparison. Personally, I'd say that a 2/1 with a solid ability is a better card than a 2/2. Or, to put this another way, how many common 2cc 2/1s with a relevant keyword ability can you name that isn't white or green? Is there a 2/1 Shroud in Blue? 2/1 First Striker in red? (Black does get a 2/1 Lifelink... but they're clearly gearing black up to be the number 3 color in efficient beaters. One look at the new zombie grizzly bear gives that away.)
It's possible that this is fair, especially considering that the power level of creatures in Magic has increased over the years. I'm much more certain that this is powerful.
I'm trying to figure out at about how far up the pick list I would draft this card... assuming the occasional artifact, but nothing too relevant. In Mirrodin, this would be first pick material... but Siluras isn't Mirrodin. If this was Magic 2012, let's say? Maybe 2-3rd pick? But that set is very fast, and a 2/1 with Haste would go a long way there. If this was Rise of the Eldarazi, however, I might shelf this card to 8-9th pick, because I'd expect it to be trumped.
Comparison made. 2/2's in white as compared to 2/1 haste in red seems about right to me actually.
Quite a lot better than Hearth Kami, though that wasn't exactly pushing the power level. Still, I feel like it shouldn't have haste; compare with Ronom Unicorn / Kami of Ancient Law.