This FAQ is for Raiden on Easy mode. It can probably get you through the Normal and Hard modes as well. If you're curious to what my time is, I'm first place with 2:58:33.

Olga - When first starting, make sure she runs right in front of you. If not, Restart. Press X and you should automatically hit her. Keep it held and you will be automatically target on her. Shoot her in the back after a second or two after you shot her the first time. She will now hide between areas, peeking out for a shot. Aim for her head. Target time: 20 seconds.

Fatman - Hurry up and equip the SOCOM. Now hurry up and equip the Coolant. Tap R to equip the SOCOM again. Run towards the right in the upper area and shoot at Fatman a few times when you first see him to knock him down. Go into first-person and shoot at his head. Stay targeted until you see stars. Shoot his head again. Run to the right bomb, tap R and disarm it. Fatman should come back after a few seconds. Shoot him a few times to knock him down, go into first-person, shoot his head thus killing him. Run to the left bomb, tap R, disarm it, and you're done.Target time: 30 seconds.

Harrier -

That's it for now. I will update this at a later date.