Continuity mistake: Near the beginning when Lee Van Cleef looks at the the wanted poster on the ticket booth at Tucumcari (just after getting off the train), there are two extra zero's drawn onto the poster (as added by the villain). Van Cleef then takes this poster away with him, and slots it under the door of a hotel room on a later scene - notice that the additional zero's have since disappeared from the same poster. (00:06:30 - 00:09:20)
Continuity mistake: Monco's and Col. Mortimer's hats are remarkably undamaged after having received six and four bullets respectively. Stetsons are not soft enough to just fly away with the bullet. There should be some holes in them. (00:54:55)
Continuity mistake: After Monco brings Sancho Perez back to Indio's hideout, one of Indio's henchmen shoots the tip end of Monco's cigar off. When Monco relights that cigar, the cigar is longer. Immediately after, Indio lights his cigarette with that cigar, and it gets shorter. (01:06:00 - 01:07:00)
Continuity mistake: When Monco drives away with the dead bandits a tail gate of the cart is swinging freely. A few seconds later - after having retrieved the money bag from the tree and driving away 'into the sunset' - the tail gate is not there. (02:04:35)
Continuity mistake: The wagon that Marco initially loads all the bodies onto - and the position of the bodies - then changes completely in the next shot as Marco retrieves the saddlebags and rides off into the distance.
Continuity mistake: When Col. Mortimer slots the poster under the door, the paper changes side between shots.
Continuity mistake: The "Man With No Name" rides out of town after collecting his reward for Cavanaugh on a red colored horse. He arrives in El Paso on a brown horse with a different saddle. After he kills the three men he was sent out with to rob a bank he mounts a brown horse but arrives at the telegraph office on a red horse. It is obvious he rode straight to the telegraph office. He leaves the telegraph office and is riding the brown horse again.
Continuity mistake: When Manco goes to the saloon in search of Cavanaugh, he is outside in pouring rain. Yet he enters the saloon with neither his hat nor his sarape wet.
Continuity mistake: When Manco plays poker with Cavanaugh, he has three aces in his hand and Cavanaugh has three kings. When Cavanaugh puts his hand down, his three kings are from bottom to top. When Manco lays his hand down, Cavanaugh's three kings are now from top to bottom.
Continuity mistake: When Manco is dealing the cards, the position of the cards dealt to Cavanaugh change over and over with each card dealt. A coin is visible on one card dealt, then it is gone on another deal. Manco's stack of cards he deals to himself also change from a neat pile to a slightly askew pile.