You can see (what I presume to be) the current concept for 16 of these things at the creature competition on WotC's site.
Creature Competition:
If you scroll down past the bracket, you can see a small picture as well as the basic flavor text/concept for each of them that was given to help people vote, such as what the Sphinx Mystery is and what not. (Though, the description for that particular one is basic enough that it could be a generic sphinx, but maybe they just needed a way to differentiate it from the entry named Sphinx already in MM1).
Creature Competition:
If you scroll down past the bracket, you can see a small picture as well as the basic flavor text/concept for each of them that was given to help people vote, such as what the Sphinx Mystery is and what not. (Though, the description for that particular one is basic enough that it could be a generic sphinx, but maybe they just needed a way to differentiate it from the entry named Sphinx already in MM1).