my tipps for thing thing arena3:
KI is very low. Enemys just run after you, if you stand right at the same place as you they can´t harm you.
They are progamed heading right to your direction if you stand at the same place as they do they won´t move and because their weaopons are a bit away from their bodys (body->hand->weapon) they can´t shoot at you. You can also try to put them below you, if you jump to a higher platform they will try to come after you but if the jump ain´t enough they walk below you and only shoot at the walls.
(P.S: Try to do 100 kills with every weapon to get most medals)