Iron Man somehow got to Metroville before the Incredibles does.
Syndrome and his Omnidroid will be facing up against Mark L armor.
No prior knowledge of each other
Syndrome can call in his mercenary army or something
Death, destruction, incapacitation, or arrest
Iron Man have to stop Syndrome and his bot while minimizing as much civilian casualties as he could. Syndrome will just have to prevent Iron Man from foiling his plan.