This guide will be straight to the point. Nothing fancy. I recommend doing it in this manner due to an intentonal quirk in Clintville which will be discussed toward the end of the guide.

Start the game as the Hero character and play the tutorial. You have to kill your brother in order to get the achievement and the only way to do that is to play the tutorial. You do not, however, need to kill the murderer, so don't worry about screwing up endings. You need to kill a total of 75 people to earn the achievement. That having been said, here is a list of everyone you need to kill and the order you should kill them in.

Family Ranch

• Brother

Uncle's House

• Uncle

After the tutorial, head east toward the ranchers and Fort Motors.

Rancher Cobbs

• Rancher Cobb

Rancher Richard

• Rancher Richard

Head north to reach Fort Motors. Allow Gen. Motors to enter the building. I'd hold off on killing them, for now. Instead, go north east until you reach Mine Entrance

Mine Entrance

• Miner's Widow

Mine Interior

• Miner
  
• Ostrich Bandito #1
  
• Hailshot Sisters.
  
• The Director.

Note: You do NOT need to enter the Bonafide Bandit hideout near the Miner's cave.

The Director is found in a hidden area called "The Fourth Wall" in the north end of the tunnels. You'll emerge onto a farm with a locked gate. Shoot the lock on the gate and hug the north west wall. The Fourth Wall has lots of cash and you can ask The Director for a clue.

The hailshot sisters can be found in the outdoors portion of the mine to the northeast. Their house borders a cave needed for the Weird West achievement. Once those five are dead, leave the mines and enter Indian territory due east of Mine Entrance.

Indian Outpost

• Indian Chief

Indian Camp

• Chief's Brother
  
• Iiniwa

From the golden buffalo statue west of Indian Camp, go south. Here you'll find Ostrich Bandito #2

Woods

• Ostrich Bandito #2

Once the bandito is dead, go back to Clintville. Ask the banker for a job and help Concerned Wife wrangle Drunk Husband. Once Concerned Wife introduces you to The Sheriff, go outside and kill Concerned Wife and Drunk Husband. There is no penalty for killing them; the people of Clintville will NOT attack you. Also, complete Teary Eyed Woman's quest and kill her once she leaves for the graveyard. This will ensure Clintville residents don't attack you.

Clintville 1

• Concerned Wife
  
• Drunk Husband
  
• Teary Eyed Woman

Go south west from Clintville, following the train tracks. Kill all of the Beefhead Bulls on the bottom floor, top floor, and exterior. Now go to Clintville Train Station and talk to the Train Master and Ticket Salesman. Reveal the Ticket Salesman's scheme and inform the Train Master that the Beefhead Bulls are dead. You MUST to do this quest as your sister won't appear until the trains are fixed. You now need to collect three volunteers. I recommend The Old Miner, Rancher Bell, and The Undertaker. Once you collect everyone, go back to the tunnel and talk to the Train Master, then go back to the Train Station and talk to the Train Master again. Your sister is now on her way. Complete any of the horseback escort missions to guarantee her arrival.

For now, go to Oil Tycoon's house, south west of Rancher Bob's.
Oil Tycoon's Mansion

• Oil Tycoon
  
• Oil Rig Manager

Shoot the Oil Rig Manager first as she is the only person in the room with a shotgun. Then turn your attention to the tycoon. As soon as they're both dead, you can leave without fighting the rest of the goons. Leaving the Tycoon's mansion, head due south. Once you've gone as far south as you can go without going into the western mountains, you'll see a little shed on the right side of the screen. It's entrance will be obscured by a tree. Go inside to find Ostrich Bandito #3.

Mountain Shack

• Ostrich Bandito #3

Travel to Santa Anna and cross the bridge to enter into the mountains. Go north one screen and use the ramp to walk into the river bed. Go north another two screens and you'll see Ostrich Bandito #4 with his three coyotes. Shoot them all from the dry riverbed to avoid having your throat ripped out.


Santa Anna Mountains

• Ostrich Bandito #4

Returning to Santa Anna, tell the Buffalo Express driver you're here for The Banker, BUT don't start just yet. Fast Travel back to Clintville and ask the Sherrif to help you with the Banker's quest. Say you "need someone reliable" to get him motivated. Return to Santa Anna and enter the Buffalo Express to find the Sherrif and The Driver
IMPORTANT NOTE: If you enter the Clintville Sheriff's Office after this, Clintville will turn hostile and you will have to start over.

Santa Anna

• The Sherrif
  
• The Driver
  
• Miss Hatt
  
• Everyone in the Saloon

Once you murder everyone in The Buffalo Express, the townsfolk will turn hostile. You can ignore them. Santa Anna does not build fortifications as Clintville does. After cleaning Santa Anna, go one screen west of the Santa Anna Train Station and as far north as you can go. Here you'll find Brit, a companion. Kill him.

Desert 1

• Brit

Return to Santa Anna Train Station and head due east, following the tracks, until you reach the train tunnel. Go one screen south. At the very bottom right hand side of the screen, you'll find the final Ostrich Bandito. He can be a bit trick to kill. If you're having trouble, buy a shotgun from the Clintville Train Station weapons dealer.

Desert 2

• Ostrich Bandito #5

Head to Rancher Bob's (it should already be marked on your fast travel) and offer to help him with the Buffalo Drive. Doing this will guarantee that your sister appears and you have nothing to lose since you already killed the beef heads. The quest will end as quickly as it started, leaving you at Fort Motors with $300. Hold off on killing Bob, for now. Walk off screen in any direction and then back on. Now kill everyone in Fort Motors, making sure to start wiht Lt Fort (the female officer standing on the wooden platform). Once everyone outside is dead, go back inside to finish off Gen. Motors.

Fort Motors

• Lt. Fort
  
• Gen. Motors

Fast travel back to Rancher Bob's and clean house. Start on the lady in red. If you open fire on Bob, Miss Tress will run off screen.

Rancher Bob's

• Rancher Bob
  
• Miss Tress

Now fast travel to the Clintville Train Station. You're sister should be there. Talk to her (but don't kill her yet) and enter the train station. You can now clean out the Train Station and the Weapon's Dealer. Unlike Clintville and Santa Anna, townsfolk will not attack you for shooting up these buildings. Kill the Train Master first as she has a shotgun and the Ticket Salesman is unarmed.

Clintville Train Station

• Train Master
  
• Ticket Salesman
  
• Gen. Store
  
• Miss. Store
  
• Hat Girl

With all those people dead, you're almost done! Head to Clintville proper. This is where it gets tricky and why I was inspired to write this guide. Once you start shooting, Clintville boards its doors and certain NPCs disappear. That is why we've saved this area for last and why we sent the Sheriff to Santa Anna.
IMPORTANT EXPLANATION: If you kill the sheriff by going into his office, the saloon's door will close, making everyone inside inaccessible. If you shoot up the Saloon, the sherrif's door will close, making everyone inside inaccessible. If you shoot up either location FIRST, the two people you need to eliminate on the street will disappear, making the achievement inacessible

To get the achievement, you need to kill Old Miner AND Rancher Bell before turning the townsfolk hostile. To do this, ask Old Miner to give you a tour of Clintville. He will first take you to the Bank, which is incidentally next door to Rancher Bell. Now you can safely kill them both without either one disappearing from your screen. You ABSOLUTLEY MUST enter the saloon next. If you go in the bank first, the Saloon will close, permenantly.

Clintville 2

• Old Miner
  
• Rancher Bell
  
• Everyone in the saloon
  
• Banker

If you did all that right, you only have two people left. Go back to your family ranch, where the game started. Talk to your sister, but don't kill her. Fast travel to Fort Motors and talk to her again. Now go the the Clintville Graveyard (2 screens north of Clintville) to find your sister talking to The Undertaker. For reasons unknown, The Undertaker will always come back to life. To ensure that didn't happen, he was the last person I killed to get the achievement. Eliminate your sister and the Undertaker to get the achievement.

Clintville Graveyard

• Sister
  
• The Undertaker

Congrats. You're the biggest star in the movie. The extras are all that's left because some murderous lunatic killed everyone else.