At the main menu, select "Exclusive Content" and enter "735S653J" to get extra money for equipment in single-player mode, silver weapons in multiplayer mode, and an exclusive weapon for the first two chapters.
Very hard difficulty:
Beat single-player mode to unlock very hard difficulty.
Skip final duel:
While playing as Thomas and fighting Barnsby, use a prime condition volcano gun or better. Wear down Barnsby, then fire all 12 shots at him to kill him and skip the final duel.
Avoid losing momentum:
Jumping and switching weapons while in mid-air is an excellent way to help keep your current speed and momentum, especially if you find yourself being chased by someone in a multiplayer game and are low or out of ammo for your current weapon.
Killing Barnsby quickly glitch:
AsThomas, equip a Volcano gun or better weapon in good condition. Wear Barnsby until Thomas can use Concentration mode, then fire all 12 shots directly into him. The game may glitch and he may die without need of the quick draw sequence. You will then view the ending.
99 Scalps - Deliver 99 headshots (ranked play counts).
Act I - Complete act I.
Act II - Complete act II.
Act III - Complete act III.
Act IV - Complete act IV.
Arkansas Fried Rooster - Blow up 10 chickens with dynamite.
Between Hay and Grass - Finish the game on at least medium difficulty.
Boy Scout - Finish one side quest.
Catcher in the Rye - On chapter II, in the field, kill enemy soldiers using knives without being.
Crime Does Pay - Win 5 rounds as an outlaw (ranked only).
Crowbait - Finish the game on at least easy difficulty.
D-Day - On chapter I, destroy all rafts before they land.
Drive-By - Kill a total of 5 enemies while horseback (ranked play counts).
Fireworks - Shoot 2 enemy dynamite sticks in mid air.
Frag Steal - Kill all enemies in a single cooperative concentration mode.
High noon - Kill 4 enemies between 12:00pm and 12:15pm (local time, ranked play counts).
Jack of all trades - Play a full game with each class (ranked only).
Mad Carpenter - Kill 5 enemies with a chair.
Man of the Hood - On chapter XII, playing as thomas, use only bow throughout the whole level.
Mayhem - On chapter III, kill 20 armed enemies while riding the stagecoach.
None shall hide - Shoot an enemy through a wall.
Pistol Expert - Kill 250 people using pistols (ranked play counts).
Quick hands - Kill 7 people during one concentration mode.
Quite a Ride - On chapter IX, on the lift, destroy everything that is thrown at you.
Rifle Expert - Kill 250 people using rifles (ranked play counts).
Rowing-Race Cheater - On chapter XI, kill all the Indians during canoe chase.
Sharpshooter Destuction - On chapter IV, playing as thomas, kill sharpshooters in 10 seconds.
Sharpshooter Distraction - On chapter IV, playing as ray, kill sharpshooters without thomas's help.
Shield of Hope - Finish all side quests.
Shotgun Expert - Kill 250 people using shotguns (ranked play counts).
Tin Star - Win 5 rounds as a Lawman (ranked only).
Unforgiven - Kill 10 enemies as an invincile wanted (ranked only).
Vindicator - Kill a total of 30 enemies with movable gatling.
Welcome to the Frontier - Finish a full wild west legends game (ranked only).
Well Invested - Buy 20 second level and 10 third level upgrades (ranked only).
Yankee Cow - On chapter II, don't kill the cow.
Been there, Done that - Play a full wild west legends game on every level (match and revenge).
Curly Wolf - Finish the game on hard difficulty.
Gotta Catch'em All - Collect all secrets.
Magnificent Thirteen - Unlock all classes (ranked only).
On the right track - Collect $200,000 (ranked play counts).
Ray's Story - Finish every chapter playing as ray.
Thomas's Story - Finish every chapter playing as thomas.
Untouchable - Finish any chapter, except for VI and VIII, without getting severely wounded.
Forgiveth Me, Lord - Kill 2000 enemies (ranked play counts).
Goldrush! - Collect $1,000,000 (ranked play counts).
Old West Legend - Finish the game on very hard difficulty.
Ace of Spades - Earn all Bronze, Silver, and Gold trophies.