Meanwhile, in America, STI worked on "Sonic X-treme", a 3D "Sonic" game for the Saturn intended for the 1996 holiday shopping season. Development was hindered by disputes between Sega of America and Japan, Naka's refusal to let STI use the "Nights" game engine, and problems adapting the series to 3D. After two lead developers became ill, "X-treme" was canceled. Journalists and fans have speculated about the impact "X-treme" might have had if it was released, with producer Mike Wallis believing it "definitely would have been competitive" with the first 3D "Mario" game, "Super Mario 64" (1996). Due to "X-treme" cancellation, Sega ported "Sonic 3D Blast" to the Saturn with updated graphics and bonus levels developed by Sonic Team.