See Lambent Incarnomancer and Transmogrify.

Seems kinda abusable, if your deck is filled with cheapish creatures, lands, 3 of this, and "Win the game, cost 7+" type of sorceries. The ability to force your opponent to explode their combo before it's ready is just icing on the cake.

This seems less abusable to me than Polymorph.

Well, the similar abuse with polymorph you need to have a small creature and a big creature and you might get the small creature again. You can get around that with token makers, but it's a bit harder to abuse.

It does indeed have the same kind of problem though.

It's easier than Polymorph because of token-makers, though. With Polymorph, a creature you want, and all of your creatures produced by tokens, you can get the same creature every time. This can reveal itself, so you can't just avoid having other possible targets.

So you want 2 or 3 creatures on the field before you cast this. Admittedly the question of what instant or sorcery do you put in is an interesting one. Time Stretch is less good if you've had to give up 2 creatures first. Emergent Ultimatum gives you the challenge of finding three components none of which is an instant or sorcery. Maybe Worldfire (with Keldon Marauders or Syr Konrad on the field) or Star of Extinction.

In order for this to be consistent in a way you can force Polymorph to be consistent, you'd have to run only one copy of this and what you wanted to pull out as your only instants/sorceries, or run lots of scry/library ordering.

If you ran only one of these, you'd need a way to tutor for it that wasn't an instant/sorcery.

That's what I was getting at when I said "2 or 3 creatures": you can play 4x this if you can guarantee having 4 spare creatures when you cast it, and you've got decent odds of getting your "target" sorcery if you have 2 or 3 spare creatures.

Oh, gotcha. I missed that on my first reading. I was neglecting to think about the fact that if you pulled this again it could just rather a spare creature.