Instructions
Fight off Radec's support troops, using your knife to finish off the enemies that drop down over the railing. Avoid shooting at Radec at this point, since he'll just teleport away when you try. Hide in the left or right side in the room by the balcony, and knife the enemies as they respawn.
Keep Rico alive. Hide from the enemies until they focus their fire on Rico, then attack them with your knife. Revive Rico if he is knocked unconscious, but wait until there's a break in the assault.
Kill the second wave of troops. Use cover to avoid Radec's fire, and shoot the troops that come at you. Hide behind the support pillars to take a breather from enemy fire when necessary. Run to the staircase and shoot the troops, then fire at the Shock Troopers as soon as they appear, and grab the Grenade Launcher from the gun rack by the staircase.
Fire your grenade launcher from the junk pile by the right staircase. Focus on Support Troopers first, before you go after the Assault Infantry. Move your position if rocket fire gets too close. Keep killing enemies until they're all gone, which triggers a cutscene that shows more troops coming toward you. Run to the right staircase to grab more grenades for your gun. Finish off the waves of troops to begin a one-on-one fight with Radec.
Grab the StA2 LMG and take out your knife. Run to the pillar in the middle of the room and run circles around it to avoid Radec's fire. Listen for his teleport noise; when you heart it, look around for a blue light to identify where he's moving to. Knife Radec as many times as possible when he gets close to you.
Stay on the offensive. Keep shooting and slashing Radec, causing him to teleport more and more. Grab new guns from the gun rack when you run out of ammo, and keep shooting Radec to finish him off.