Red Dead Revolver Cheats

Completion bonuses:
After finishing the game you will unlock bounty hunter mode and hard mode.

Finish the game in "Hard" mode to unlock the "Very Hard" and "Red Wood Revolver" (play as Manny Quinn training dummy) modes.

Buy every item from the stores to unlock all showdown characters and journal pages.
User Cheat by Nightcrawler

Cheat mode:
Play through the game in bounty hunter mode to unlock various cheats, including "Invincibility", "Infinite Deadeye", "Golden Gun" (powerful guns), "Bite the Bullet" (one hit kills), "Sad Stars" (blood replaced with stars), "No HUD", "No Distortion", "Show Player Position", "Show AI Info", and "Big Money" at the pause menu; as well as more characters in Showdown.

Chapter 1: Morning Star (Red's mother) as a showdown character
Chapter 2: Sad Stars cheat
Chapter 5: Sheriff Bartlett as a showdown character
Chapter 11: Smitty as a showdown character
Chapter 14: Matilda as a showdown character
Chapter 18: No HUD cheat and Grizzly as a showdown character
Chapter 20: Bite the Bullet cheat
Chapter 21: No Distortion cheat
Chapter 24: Infinite Deadeye cheat
Chapter 25: Golden Gun cheat
Chapter 27: Invincibility cheat

Quick reload:
When you get knocked down, press Y and your gun should reload before you get up.
User Cheat by Jeffrey

How to beat Bosses:
To kill the majority of Bosses, use height to your advantage. There is more often than not a location where they cannot get to you and will stay in range.

Unlock Manny Quinn:
REMEMBER: This is the most difficult task in the game. You must first unlock everything, including the lucky flask from talking to jack swift in Brimstone (the third time you visit); the pocket watch from the paperboy in Brimstone (the fourth time you visit),.and the hot bath from the girls in the tub upstairs during the saloon fight. You must also achieve an "Excellent" rank in every chapter by either earning three stars or purchasing items until there are no "Excellent" locks left to open. After finishing your game and achieving the above, go to "Showdown". You must have all 47 characters unlocked and 99% of game completed before proceeding.
User Cheat by Pontius

Secret shop:
In the beginning of the level after you play as Shadow Wolf, turn around and go back to the jail cell that you and the Buffalo Soldier were in. You can talk to the skeleton. The shop menu will open, and you can buy a horseshoe and snake oil.