Head to the bottom of the stairs from the escape route to reach the next area. When you reach the bottom of the steps, Tyrant will burst through the wall and attack you. It doesn’t matter if you defeated Tyrant earlier; he will still pop through the wall here. The big difference is that, if you defeated Tyrant earlier, he will be weaker here than he would be if you had not. This makes killing him for a second time a feasible option, but only if you have a full squad of four players with plenty of grenades and ammo each. Remember that almost right after you fight Tyrant here, you will be thrust into battle against Nemesis. This means that you really can’t afford to waste a lot of health or ammo (although decent supplies of both will be in the arena with Nemesis.) The narrow corridors of this area can also make it difficult to challenge Tyrant. If you defeat him again, you will get the same handy 1,000 experience point bonus as you did before, though.
Whether you killed Tyrant or decided to run, head for the exit door. Along the way, search to the side to find the last two pieces of Intel and a Laptop to upload them from. The exit door will take you to the reception area where you first started out. You will find some ammo here, and picking it up will be an absolute necessity if you decided to fight Tyrant for a second time. Grab it and board the lift to climb back up to the warehouse area. Here, you will find Nemesis still engaged in battle with the Spec Ops soldiers.
Boss Battle: Nemesis
The arena in which you fight Nemesis will be split up into two levels, the ground level and the upper level. The ground level, where you will begin, is dotted with cover in the forms of boxes and crates scattered about, as well as the elevator shaft to your left from where you enter the room. The upper level will be connected by a series of thin planks and beams, and will form a sort of balcony that circles around the perimeter of the room. This upper level will be where most of the ammo is stored, but also where the majority of the fodder enemies will spawn from.
Nemesis will stand in the center of the ground level, firing his chaingun at all who dare to oppose him. Your objective during this battle will be to weaken Nemesis sufficiently to inject him with the virus that you extracted from Tyrant, thus handing control of him back over to Umbrella. You will know that Nemesis is ready to be injected when he falls to one knee. This is your cue to sprint up to him and hit the action button. Because you will have to be fast about injecting Nemesis, you will probably want to stay on the ground floor for the majority of the battle, only heading upstairs to refill your ammo.
Nemesis may be tough, but he is far from the smartest enemy that you have faced. During this battle, he will barely ever move of even attempt to flank you while you are in cover. You will begin the battle behind a stack of crates. This stack makes for good enough cover during the first portion of the battle. If you have multiple human squad members, they won’t all be able to fit comfortably behind the stack of crates. In this case, have one player take cover behind the crates, make a second player take cover in the elevator shaft to the left, and have the other two players head up to the upper floor to provide covering fire to those below. As mentioned earlier, infinite waves of zombies will swarm in from the upper floor, so those players should try to keep on the move as much as possible as this area isn’t all that safe. With four players hitting Nemesis from four different spots, he won’t know where to focus his gunfire and he will be largely useless.
While you are firing, try to back Nemesis up towards some of the explosive barrels littering the floor. He will begin the battle near one of them, and midway through the fight he will move towards several others. Hitting him with one of these powerful explosions will take away a pretty significant chunk of health from the boss.
If you have been stockpiling Incendiary Grenades, now is the time to use them. Toss all that you have onto Nemesis. His weakness to fire will end up biting him in the end, as these grenades will deal tons of damage to the heavily armored enemy. When you run out of Grenades, note that there are four more located throughout this arena. Four of them are Frag Grenades and are located along the perimeter of the upper floor balcony, while the fifth is a valuable Incendiary Grenade found on the ground floor. Healing items are also strewn about on the ground floor, so look here first if you desperately need to heal. If you are dying and out of health, remember that zombies will sometimes drop healing items when killed. If you are playing as a Medic, you can easily perform a Brutal Melee Kill on one of the enemies to make a Green Herb pop out of them.
After you have weakened Nemesis significantly, a squad of Spec Ops soldiers will burst in through the lower floor. These enemies are easily distracted, so try to keep their focus on Nemesis, not you. Stay out of their line of sight and allow them to help you weaken Nemesis if possible. Only kill the Spec Ops soldiers if it is absolutely necessary, because they can actually be a big help, especially for solo players.
When you have dealt enough damage, you will see Nemesis drop to one knee. This is your cue to rush in and attack with the syringe. Ignore all of the enemies in your path; they won’t be a problem once you inject Nemesis with the syringe. When you have completed this goal, a cutscene will play and the mission will end.