When the Nova labs were destroyed they were done so by a mysterious fire, the cause of which wasn't explained. Perhaps an opposing group against WAR decided to destroy the place and took the Nova plans for themselves before destroying it, all while the 2097 tournament took place. The group of which who did and for what purpose they stole the plans, god only knows. Iron Fist? A WAR splinter group? Someone else?
Rough sketch of Mantas Robot. I also included a side view of the leg and made it more insect-like with 3 sections. Just an idea. The leg can easily be changed to a standard bipedal type leg.