Scientists | Scientists spawn in light containment zone, way before chaos will spawn.
C.A.S.S.I.E will mention Mobile Task Force have entered the facility on the announcements. You will know if MTF spawns or if they are about to spawn by: seeing a helicopter about to land at surface Gate B or if you hear announcement by C.A.S.S.I.E.
They will go down gate B, which is relatively close to gate A, so it is once again advised you do not stay in entrance zone for too long. These guys also spawn in big waves, so it is advised you do not attempt to solo them or attempt to kill them in a small team. MTF (Mobile Task Force) | MTF spawn at the opposite side of the map from where you spawn, at Gate B. Your enemies as a chaos insurgent may differ, depending on your situation, but here is a list of your main enemies:
