Elite Guard #1: After dropping down to the destroyed walkway early on in the mission, check behind you for this Elite Guard.
Elite Guard #2: In the main area, use one of the launch pads to reach the big rock formation with a Rune Trial on top. Check your map to spot a sneaky low ledge on the side (far below). Crouch and use the map to align yourself correctly, then carefully drop down and use a double jump to reach a Megahealth and this Elite Guard.
Elite Guard #3: After activating the Pinky hologram and following it outside, clear out the demons in this area and use the launch pad to reach the upper platform where this Elite Guard is located at.
Elite Guard #4: After finding the yellow keycard, drop down the elevator shaft. Check for a ventilation shaft inside the elevator shaft to find this Elite Guard.
Rageguy Collectible: At the first big platform, during the beginning of this mission, spot the pillar with the number 1 on it. Simply check the left side of the area for the Rageguy.
Patriotguy Collectible: After finding the yellow keycard on the Pinky, and before jumping down the elevator, check the bloody ledge just above the small steps and double jump to it. This secret area contains Patriotguy.
Classic Map: At the beginning of the mission, where you find Rageguy, climb all the way up and check behind the crates to find a lever. Go back down to find the entrance to this map behind the pillar.
Argent Cell: In the landing platform area with a vehicle in the middle (and where you fight off a large demon horde), face the door you should pass through and turn right. Climb the stone rocks and descend a little to find this Argent Cell.
Field Drone: In the area with the Megahealth, near the end of the mission, use the console near the lower walkway to activate a container, moving it above the walkway. Climb it to reach a walkway to the right, where this Field Drone resides.