Old World Blues (quest)

Old World Blues is a main quest in the Fallout: New Vegas add-on Old World Blues. During this quest, you'll earn the "Make up Your Mind" Trophy/achievement. You'll be rewarded with "Outsmarted" after you finish the quest.

Quick walkthrough

 * 1) Talk to Dr. Klein.
 * 2) Enter the Forbidden Zone Dome Entrance.
 * 3) Defeat/disable the X-42 Giant robo-scorpion.
 * 4) Enter Mobius' lair and reason with or kill him.
 * 5) Reclaim your brain.
 * 6) Reason with/defeat Think Tank.

Detailed walkthrough
You'll start this quest by speaking to Dr. Klein, He will tell you that it's time you went to the Forbidden Zone Dome Entrance, and get your brain back. He also asks you to deal with Doctor Mobius.

You'll start by traveling to The Forbidden zone, there you'll encounter a few Robo-Scorpions, After dealing with them and entering the zone itself, Dr. Mobius will release his latest Experiment, X-42 Giant Robo-scorpion. You can either fight it, or enter the room to the right and use the terminal to access turret controls to turn it upon the Giant Scorpion. Farther to the right, there are stairs that lead to a terminal, which gives the option of activating the scorpions backup generator, overloading it, and causing some damage. There is also a balcony room, in the far left side of the zone from the entrance, that contains a Very Hard computer terminal. If hacked, it gives the option to permanently disable the X-42 Giant Robo-scorpion. Access to this room is via the stairs in the far left side of the room. This may make accessing it without taking much damage difficult without a stealth boy or sneaking, as the X-42 Giant Robo-scorpion is between the entrance and it, however, activating the Protectron test drones in the room to your immediate right upon entering will distract it long enough to get to the shutdown terminal. Alternatively if you have the Robotics Expert perk, you can just sneak up on it and disable it.

After defeating it, you must proceed to confronting Dr. Mobius, and recovering your brain, simply take the stairs to the left of the entrance and make your way to the door on the right. There you'll meet Dr. Mobius, he's not hostile, and here you have 2 choices: reason with him or kill him. If you choose to reason with him, he'll direct you to your brain and ask you to convince it to join back with you. You must then speak to your brain, and you have to convince it to join you again. Having high medicine/science will give you a slight advantage and make your dialogue much easier.

After acquiring your brain, you have to talk to Dr. Mobius again, He'll tell you more about what the Think Tank is all about and suggest you deal with them, instead of himself, The choice is yours of course. After making your choice, simply travel to the Think-Tank. There you'll have to either Fight or reason, In order to reason, you must have either 80 in Speech skill, 85 Medicine, or 100 science.

Alternatively if you completed the side quests What's In A Name?, On The Same Wavelength, A Brain's Best Friend, and Coming Out of Her Shell. You can tell Klein to confer with his colleagues, which allows you to reason with the Think Tank without using the high skill checks. After completing the quest, and watching the ending slide show, the player is given Big Mountain Transportalponder! Upon completion, all active personalities in The Sink will cheer for the Courier's victory, with a particularly drawn-out and rambling congratulations from Blind Diode Jefferson.

Bugs

 * Watch out what you say to your brain. When you ask it if it wants to be reunited, and then choose the compromise option, do not choose the second choice if you have completed Come Fly With Me and That Lucky Old Sun; you can get caught in a never ending loop of him talking about the quests. You cannot get out of this loop unless you reload a previously saved game.
 * Before entering the Forbidden Zone Dome, it is advisable to make a new separate save as when entering through the main entrance into the arena with the Giant Robo-Scorpion, it is possible to load under the catwalk and become stuck there.
 * Be mindful before completing the quest and make a save somewhere outside the Think Tank. When the quest is completed and you are asked to leave Big Mt, the moment the slideshow starts the game crashes. This forces you to reload an earlier save. If last save is inside the dome, you will be trapped.
 * After finishing this quest by either killing or talking to the think tank, your game may crash as you try to leave (this has been an ongoing bug for me, I am currently unable to finish Old World Blues because of it, will post a fix as soon as I find one)