In April 1999 issue of Official US PlayStation Magazine I found this: I don't recognize developer - Syrox??? And only released Activision X-Men games were X-Men Mutant Academy and X-Men Mutant Academy 2 made by Paradox Developmen. Was this early version of first Mutant Academy or unreleased canceled separate project?
IGN articles is the only good thing of IGN and any other digital magazine that comes to my mind, they come handy sometimes. http://www.ign.com/articles/2000/07/06/x-men-mutant-academy-4 Long story short. Its X-Men: Mutant Academy. It was initally developed by Cyrox (i think the magazine is wrong with the name) and planed as free-camera arena-fighting game like Tekken or Dead or Alive. But they never accomplished something decent and Activision, the producers, hired Paradox to start the final project, a pseudo-3D fighting game with fixed-depth camera.
The final versions of the X-Men Mutant Academy games used a 2 player version of the Thrill Kill engine.