I've watched the first 34:30 and have made the following summary of what I've seen.
The beginning is simple enough. An imposter Sartana goes to the bank to collect a bounty on an outlaw Bill Cochran. The bank teller checks on the body, only to find that Bill Cochran is still alive. Together Sartana and Bill, and another hold up the bank. Some fake bank guards/soldiers also help out and shoot the real guards. The fake sartana is apparently using the same multibarreled derringer that the real sartana uses, and accidently drops the cylinder on the ground. During the ruckus, the bank owner is knocked out. The sheriff identifies the fake sartana as the real sartana.
The next scene isn’t so clear: The fake sartana, who’s face is unseen, along with the rest of the bank robbers are in their hideout. A little fight appears to be brewing when one of the men demands to divide the stolen immediately. Suddenly, an unknown person (either the real or fake sartana) shoots all the people dead. The fake sartana survives.
Three bounty hunters, including Gordon Mitchell and Klaus kinski see the new wanted poster with sartana’s name on it.
Sartana meets up with the bank owner at his home, who is still recovering from getting knocked out. The owner is convinced that sartana was behind the robbery, pointing out that he saw the cloak and hat but Sartana explains to him that anybody can pass as sartana.
Meanwhile Sartana visits his friend, a thief named buddy ben is in his hideout. Sartana tells buddy that the robbery wasn’t him, and at the same time, buddy ben denies framing him. Buddy offers to help him out and gives sartana some info. The yellow smoke the bank robbers used came from a guy called dynamite butch.
Sartana goes to see dynamite butch, only to find him dead. Sartana gets attacked by an Indian bounty hunter but manages to kill him. Before he dies, the Indian tells sartana that Bill Cochran has been arrested. Buddy ben shows up they talk about Bill Cochran.
Sartana arrives in town and a posse has collected to kill him, but he manages to sneak inside the saloon and starts a poker game. He plays with the newspaper editor who tells him that Bill Cochran is being held in the sheriff’s office. Sartana calls in the sheriff. Sartana wins the game and the gamblers sans the newspaper editors attacks hin but gets killed. The sheriff comes in and sartana voluntarily lets himself get arrested so he can speak to bill cochran, who is in jail with him.