After you deal with the parasite attack, return via the stairs to the middle level of the lab and cross the bridge to the surgery area. Your waypoint will be plastered on a door, but be warned that a boss battle (or escape sequence, should you choose to avoid Tyrant instead of battling him head on) will trigger once you try to activate the door. Reload all of your weapons and heal yourself if you need to before accepting the prompt to examine the door.
Tyrant will rise from the gurney and begin to stalk you through the lab. The door, unfortunately, will be locked, only to be opened by three Keycards. Tyrant is extremely powerful and can kill an uncoordinated squad in direct combat pretty quickly, but it is possible to bring him down. If you do kill him, you’ll save yourself some trouble later and earn 1,000 experience points to boot.
Boss Battle: Tyrant
This section of the guide is for those who want to try their hand at bringing Tyrant down, rather than avoiding him. That strategy, which is perhaps best adopted by players in single player or those who used their Grenade Launcher too early, will be covered after this section.
If you still have the Grenade Launcher from earlier in this level, you will want to use it now. You will have to time your shots carefully, though, because you might end up missing or dealing minimal damage if you shoot improperly. Wait until Tyrant pauses to assess the area, or until he is vulnerable after attacking. Aim high with the Grenade Launcher; you should try to hit the enemy either in the head or in the chest. You will know that you have landed a successful hit when you see the massive enemy go tumbling backwards. Empty all of the grenades in your Grenade Launcher in this manner. When you have no more ammo for the Grenade Launcher, ditch it for another weapon and start tossing regular Grenades at Tyrant if you have any. Don’t waste any Incendiary Grenades on Tyrant because you will still need these for a battle against Nemesis later in the level. Otherwise, feel free to let loose with what you have.
Once you run out of Grenade Launcher ammo, or if you never had it in the first place, you will want to aim for Tyrant’s head with whatever primary weapon it is that you can dig up. The rest of its body is invulnerable to normal ammunition, so shoot carefully. Tyrant will occasionally try to protect his head with his arms, which cannot take damage. Keep backing away from Tyrant and firing your weapon as you go. You will want to keep a good distance between yourself and the massive enemy, as many of his attacks can be incredibly damaging if they land. Tyrant will use four main attacks against you. The first is a charge attack, in which he will rush you and deal heavy damage. Use the dive move to get out of the way of this attack quickly. Next is the ground pound attack, which will knock you off of your feet if you are unlucky enough to be caught in the radius of the blast. If you see Tyrant gearing up for a ground pound move, either sprint or dive in the opposite direction. The third attack is a grab move. This will only occur when you are close to the enemy. Tyrant will grab you by the neck and hold you in the air with one hand, slowly choking the life out of you. You will pull out your Pistol and have to shoot Tyrant in the head repeatedly to make him disengage before you die. The final of Tyrant’s attacks is a simple punching move. This attack is the easiest to avoid because you can just sprint out of its radius before it connects.
You won’t just have Tyrant to worry about, though. Parasites and parasite zombies will be swarming the area during the whole battle, especially if you accidentally get too close to one of the Keycards and activate an enemy spawn. Tyrant’s constant approach makes it nigh impossible to create a chokepoint and make a stand against the enemies, so you will want to constantly be one the move. Avoid the waypoints on the mini-map, as large numbers of enemies will spawn from them when you get close. Instead, just focus on making a circle around the map, down the stairs to the lower levels, then back up the stairs and across the bridges.
If you are playing with multiple players, you can distract Tyrant with one player while the others circle behind him and shoot him in the head. Another strategy to use when playing with multiple human players is to send part of your team off in search of the Keycards while the other part of your team works on defeating Tyrant. This way, if you find yourself in a sticky situation, you can escape through the lab door without having to run around hunting the Keycards first.
Locating the Keycards
If you opt to find the Keycards instead of battling Tyrant, you will probably have an easier time, although you will have to do it fast because Tyrant and the various enemies swarming about will kill you if you don’t. Whether or not you decide to kill Tyrant, you will have to get the Keycards at some point or another. Each card will be marked off on your map by a waypoint, so they shouldn’t be too hard to find. Head to the top level and inside of the central lab where you saw the first parasite to find the first, along with a parasite zombie. The second card is located behind the door by the entrance. You will find Intel to the left of the Keycard as well. When you pick up the Keycard, a group of zombies will crawl into the previously empty room, so turn around and sprint away to escape. The third Keycard will be on the bottom floor, in a janitor’s closet in the very back of the short corridor. Open the door and toss a grenade inside, or use an automatic weapon, because the closet will be packed with enemies. You can pick up a piece on Intel from the table to the right and a First Aid Spray from the floor before you leave. Proceed to the door and use all three keycards to escape.