This card reads a lot worse than it is (it's actually very good in limited, and probably usable in block). Originally supply creatures couldn't supply themselves, but it was changed for a multitude of reasons. I don't want to flat out prevent a creature from supplying itself (except in this one design), but I want there to be incentives not to.
There is a group that doesn't like that this can't supply itself, and a group that really likes the design. I know that this has internal dis-synergy that turns some people off, that's why there's only one of these.
Also, since the balance of this came up, you cannot have a 6/6 flier at uncommon (less so common). This fits perfectly in the niche I want (3/3 flier for 5 with a good upside). Yes, it's sort of a bad moment when you can't use him to his fullest, but you can't always use cards to their fullest. The "bad" result you get out of this is still a perfectly fine card in limited.
Instant speed seems like a bad idea to me. People will hold it in their hands for a trick and the card would rarely do what it was intended to do... give a creature Haste.
On a separate side note, after I got done whining like a little schoolgirl, I started thinking about how awesome a 6/6 Flyer for would be at common. Hilarious. I added it to my set to get people to argue about whether it is worth drafting or not, so thank you for that bit of inspiration, Wolfer.
You could solve your Supply issue by rewording it to say "other than itself" using the proper wording of course.
This would add 3 words to the reminder text bumping up the wordcount but it would do what you want it to do that way rather than the counters being dumped on the supply creature.
Also, substitute flash for flying and the card would be even more flavourful and playable. for a permanent Giant Growth and a 3/3 body is a pretty good deal. Or you could bump it to rare and have both flash and flying - awesome.
Agree with cgasparoni. Not being able to put counters that he supplies on himself makes me frown. I definitely wouldn't put 4 of this guy in the same deck, and would avoid putting many guys with supply in the same deck as him... which I assume would be the point of the set. I love stress in mechanics, but this card isn't a puzzle to solve. I'd rather see an overcosted 6/6 flyer.
I did say still susceptible to being stifled :P But my point is its generally fairer than "T: Blitzing Goblin deals damage equal to its power to target player."
Although it doesn't target which may occassionally be relevant :O
True enough. It is, however, just as capable of being stifled since the spell Stifle counters activated and triggered abilities (the word 'When' tells us that this ability is a triggered ability and goes on the stack). In fact, Stifle would be disasterous to this creature, since it would be subsequently blocked.
Not really. Tap activated abilies are far more abuseable than attack triggered abilities. And since triggered abilities still use the stack its still susceptible to being stifled and as attacking is the trigger and the remove from combat comes after the damage on resolution its now open to whites removal effects that deal damage or exile attacking creatures
This seems like an effect that should not be playable as an instant. Does it lose much as a sorcery? If you really want to keep it at instant, I think the CMC needs to go up to 6.
Yeah, this is stronger than Nekrataal easily it should probably destroy non-black to make it a little less crazy
Powerful enough. I would play this over Nekrataal.
This card reads a lot worse than it is (it's actually very good in limited, and probably usable in block). Originally supply creatures couldn't supply themselves, but it was changed for a multitude of reasons. I don't want to flat out prevent a creature from supplying itself (except in this one design), but I want there to be incentives not to.
There is a group that doesn't like that this can't supply itself, and a group that really likes the design. I know that this has internal dis-synergy that turns some people off, that's why there's only one of these.
Also, since the balance of this came up, you cannot have a 6/6 flier at uncommon (less so common). This fits perfectly in the niche I want (3/3 flier for 5 with a good upside). Yes, it's sort of a bad moment when you can't use him to his fullest, but you can't always use cards to their fullest. The "bad" result you get out of this is still a perfectly fine card in limited.
Instant speed seems like a bad idea to me. People will hold it in their hands for a trick and the card would rarely do what it was intended to do... give a creature Haste.
On a separate side note, after I got done whining like a little schoolgirl, I started thinking about how awesome a 6/6 Flyer for
would be at common. Hilarious. I added it to my set to get people to argue about whether it is worth drafting or not, so thank you for that bit of inspiration, Wolfer.
You could solve your Supply issue by rewording it to say "other than itself" using the proper wording of course. This would add 3 words to the reminder text bumping up the wordcount but it would do what you want it to do that way rather than the counters being dumped on the supply creature.
Also, substitute flash for flying and the card would be even more flavourful and playable.

for a permanent Giant Growth and a 3/3 body is a pretty good deal. Or you could bump it to rare and have both flash and flying - awesome.
Agree with cgasparoni. Not being able to put counters that he supplies on himself makes me frown. I definitely wouldn't put 4 of this guy in the same deck, and would avoid putting many guys with supply in the same deck as him... which I assume would be the point of the set. I love stress in mechanics, but this card isn't a puzzle to solve. I'd rather see an overcosted 6/6 flyer.
Oops. My apologies for glossing over.
I did say still susceptible to being stifled :P But my point is its generally fairer than "T: Blitzing Goblin deals damage equal to its power to target player."
Although it doesn't target which may occassionally be relevant :O
True enough. It is, however, just as capable of being stifled since the spell Stifle counters activated and triggered abilities (the word 'When' tells us that this ability is a triggered ability and goes on the stack). In fact, Stifle would be disasterous to this creature, since it would be subsequently blocked.
Not really. Tap activated abilies are far more abuseable than attack triggered abilities. And since triggered abilities still use the stack its still susceptible to being stifled and as attacking is the trigger and the remove from combat comes after the damage on resolution its now open to whites removal effects that deal damage or exile attacking creatures
I like the card. But I find it funny that it pretty much reads "
: Blitzing Goblin deals damage equal to its power to target player."
Very cool. With a critical mass of cards with supply, this could be a bomb in limited.
This seems like an effect that should not be playable as an instant. Does it lose much as a sorcery? If you really want to keep it at instant, I think the CMC needs to go up to 6.