The Superhuman Gambit

The Superhuman Gambit is a side quest in Fallout 3 as well as an achievement/trophy.

Quick walkthrough

 * 1) Go to Canterbury Commons and witness The AntAgonizer and The Mechanist fight. Talk to Uncle Roe.
 * 2) (Optional) Talk to Derek Pacion and ask about strengths and weaknesses of the "super heroes".
 * 3) Talk to the Mechanist in the his forge.
 * 4) Talk to the Antagonizer in her lair.
 * 5) Choose a side: Mechanist, AntAgonizer, or neither.
 * 6) Depending on your choice, kill one person and bring their armor to their counterpart. Then convince them to cease antagonizing Canterbury Commons.
 * 7) Alternatively, kill both of them.
 * 8) Tell Uncle Roe that the problem has been solved.

Detailed walkthrough
The town of Canterbury Commons has become the battleground of two self-proclaimed "superheroes" - the AntAgonizer and the Mechanist. Its residents are not very happy about it and ask you if you can help them.

Upon arriving in Canterbury Commons, the AntAgonizer and the Mechanist will be engaged in a standoff. After a few scripted opening semantics, the two will engage in a brawl. Once the dust clears, both will run away, and Uncle Roe will speak to you, asking you to handle the ordeal. With a Speech check, you can double the pay, from 200 to 400 caps. After you have accepted the quest, speak to Roe's nephew, Derek Pacion. Derek is obsessed with super heroes and gives you the best info on where to find the two. The AntAgonizer lives in a cave north of town and the Mechanist lives south of town in an old robot factory. (Both locations will be marked on your map.) With the Child at Heart perk, you can ask Derek for their weaknesses. The Mechanist doesn't harm the innocent, and other than the royal guard, the AntAgonizer's ants are weak.

AntAgonizer's Lair
If you decide to take out the AntAgonizer, you head to the AntAgonizer's Lair north of town. Go down the stairs and to the right is an empty room. A button on the wall lowers a staircase to a cave. Continue through the cave to the AntAgonizer's lair.

Alternatively, you can sneak in the back entrance - a pipe to the west of the entrance at the top of the same mountain of rocks that the main entrance is on (requires a lockpick skill of 50.) This route bypasses all of the ants in the tunnels. It is also possible to use this entrance if you pickpocketed the AntAgonizer's key during the brawl when first entering town.

Once in her lair, there are no ants to fight, just the AntAgonizer. There are several ways to interact with her at this point:
 * If you have already received the Mechanist's costume and are wearing it, after a brief introduction she will attack the player, believing you to be the Mechanist.
 * If you have The Mechanist's costume, but are not wearing it, you have the option of giving it to her. You will be awarded with the Ant's Sting, a unique knife, and negative karma (as she remains a delusional "super villain").
 * By attacking her or speaking with her and being aggressive, you can engage her in battle. Killing the AntAgonizer will not affect your karma even though she is an evil character.
 * Speaking with her, you can choose to help her destroy the Mechanist. The Mechanist will barge into her lair and you'll have to fight him.
 * With the Lady Killer perk, (coupled with her real name given to you by Joe Porter) to convince her see the error of her ways. After success, she will give up her career as a super villain, hand you her costume and leave quietly.
 * If you have been to Hubris Comics and read the note to the editor about AntAgonizer's cancelled Grognak the Barbarian comic, you can use this to point out that she can still be redeemed. Doing so will yield good karma. This bypasses the gender-specific perk and means you don't need to make the very tough speech check. You will also receive her costume.

Mechanist's Forge
The Mechanist's Forge is located just south of town on higher ground, inside the robot repair center.

To reach his hideout without having to fight through his robotic security, you can lockpick the elevator near the entrance with a Lockpick of 75 or above, bypassing the heavily guarded stairs. Otherwise, the facility is broken up into four sections: the office Office (left of entrance), two maintenance areas (Sector A and B, which are connected by a control room on the upper level) and the Forge (where the Mechanist is hiding). Sector B is closest to the entrance (metal door past the elevator), and the Forge entrance is on the upper level of Sector A.

The security terminal for Sector B is in the control room on the upper level, which allows you to disable the automatic turrets and security robots. The security terminal for Sector A is located in a small control room near the back of the bay, close to the Forge entrance (upper level). From this terminal, you can disable the automatic turrets in this room, as well as emit an emergency pulse explosion that will destroy any active robots in this sector.

Once you enter the forge, activate the coffee maker to reveal the Mechanist's lair. You then need to activate one of the little gears to the right of the door.

Once in the Mechanist's lair you have several options that echo the interactions with the AntAgonizer:
 * If you are wearing the AntAgonizer's costume, he will believe you to be her and attack you.
 * If you are not wearing the AntAgonizer's costume, but have it in your possession, you may give the costume to the Mechanist. The Mechanist will give you Protectron's Gaze, a unique laser pistol, and you'll receive negative karma (as he remains a delusional "superhero"). It can not be obtained by killing him; his body only holds a normal laser pistol when looted.
 * Attacking the Mechanist or using threatening speech, will of course result in the Mechanist turning hostile and fighting you. Killing the Mechanist does not result in negative karma.
 * If you choose to help him defeat the AntAgonizer he will say something about her attacking the forge. You will then have to follow the Mechanist and help him defeat her and her ants.
 * Convincing the Mechanist to end his superhero career and leave the town alone will grant you his suit and positive karma (like with the AntAgonizer, it is a very difficult speech check).
 * Either the Black Widow or the Child at Heart perks give a dialogue option to tell him he is scaring the whole town. With that, he will give you his suit and leave (if you have both perks, only the Black Widow dialogue choice will be available). This also results in positive karma while allowing you to bypass the speech check.

Completion
Once you defeat either the Mechanist or the AntAgonizer, return to Uncle Roe to receive 200 caps (400 if you passed the prior Speech check). If you speak with Uncle Roe after dealing with just one of them, the other will disappear. If Uncle Roe has been killed somehow, talking to Derek Pacion will also allow you to claim your reward.

Should you succeed in talking both of them into ending their "careers" (or just leaving Canterbury Commons) you will receive 200 more caps; 400 if you didn't succeed in the Speech attempt when given the quest, or 600 if you did.

Alternatively, you may kill one or both immediately upon entering town. Doing this grants you 400 caps from Uncle Roe (without ever needing a speech check).

Bugs

 * If you enter Canterbury Commons and kill either the AntAgonizer or the Mechanist immediately (or both), Uncle Roe will thank you and give you 400 caps but you will not get the achievement and Three Dog will continue to report on the situation at Canterbury Commons as though neither the AntAgonizer nor the Mechanist have been killed. Going into Uncle Roe's House before they are finished fighting and receiving the quest first seems to fix this problem.
 * Sometimes the Mechanist's sentry bot will stay in the same position for the rest of the game; it can be handy as it makes a very efficient guard for the town.
 * Reverse-pickpocketing a suit from either the Mechanist or AntAgonizer and giving it to the opposing party will update your quest status to "Report back to town for your reward" (as should normally happen). However, speaking to Uncle Roe will not reveal the normal dialogue choice to end the quest and receive your reward. This can be circumvented by killing either the Mechanist or the AntAgonizer, or both.
 * Upon entering the Mechanist's forge after completing the quest, he will not appear where he should.
 * If you do not stay to watch the event between the AntAgonizer and the Mechanist, and then immediately speak to Uncle Roe, all three characters may disappear. If this occurs, the quest cannot be finished.
 * When you team up with the Mechanist and have to defend the Forge, he may wander off and disappear. When you talk to Uncle Roe after killing the AntAgonizer, it shows you that the Mechanist has died; therefore you are unable to receive the Protectron's Gaze.
 * After you convince the AntAgonizer to leave, she will travel to Megaton. If you have blown up Megaton before this quest, she will enter through a door inaccessible to the player, meaning that the optional objective to kill her is impossible to complete.
 * If you passed the speech check with The Mechanist and you turned off the turrets in sector A instead of destroying them they will become hostile towards The Mechanist and kill him. If you reach the terminal before/after they kill him, it will show the turrets as still being disabled.
 * If you kill the Protectron in the Forge and then choose the fight dialogue with the Mechanist, it will revive itself and defend the Mechanist as usual.