Create a token that's a copy of target artifact or creature you control, except it's an artifact in addition to its other types. That token gains haste. Exile it at the beginning of the next end step.
So, turn 2, I cast Riddleform. Turn 3, I cast Saheeli Rai, a noncreature spell, and elect to have Riddleform become a 3/3 Sphinx creature with flying.
Though it would be a legal target, I don't think it is an intelligent target for the -2. Does the token come in only with the copiable values, making it not a creature?
As a tangent, suppose it's later in the game, with Saheeli Rai and Riddleform in play. I cast noncreature spell A, electing to make Riddleform a creature, and then use Saheeli Rai's -2 to make a token that is a copy of Riddleform. If I cast a second noncreature spell, can the token then become a creature?