Your or All non-sphinx? Because the former is a drawback worthy of making a cheapish body (though still an irrelevant drawback, since you're going to have no non-sphinx spells) while the latter is effectively an evil land-removal spell and make this way undercosted in my opinion.

How is this land removal? I don't find it to be much worse than Grand Arbiter Augustin IV or Thalia, Guardian of Thraben.

Well no; they're all the same kind of "My opponents have one less mana now!" effect.

If it hits you too, it at least looks like it might sometimes be a drawback too. But it's still a pretty good upside, on a pretty good body, for not very much mana.

Not saying it's unfair; just seems surprisingly strong.

I agree the effects of this seem to be broadly positive or at least neutral for the caster, and so it doesn't really seem to deserve the above-the-curve size (4/3 flyer for 4 mana).

I think that if it was for a different tribe, it would be much stronger. However, there aren't that many Sphinxes, and most of them cost more than five mana, so I don't think building a Sphinx tribal deck is going to get you very far. I also invite comparisons to Lodestone Golem.

What about Argent Sphinx? Or Conundrum Sphinx, for that matter?

Hmm. True, I guess; 4/3 for 2UU isn't as above the curve as it used to be a couple of years ago. It is kinda silly how blue gets more aggressive creatures at a lower rarity than any other colour: white gets 4-power flyers at mythic (Indomitable Archangel and Sublime Archangel), but blue gets them at rare.

I guess blue's aggro decks have to be careful to not shoot themselves in the foot. I'm just used to thinking of blue being more along the lines of Mahamoti Djinn.