You have to pester the colonel on the codec like 3 or 4 times until he gives the idea to plug the controller on slot 2. The first few times I got past Mantis thanks to infinite ammo and health, brought to me by Gameshark 🦈. If you keep shooting the FAMAS, a shot will occasionally hit Mantis. He dodges explosions, so Grenades, Nikita and Stinger don’t work.