The Night Dr. Loveless Died - S3-E4
Continuity mistake: In the opening scene, a cowboy sitting atop the balcony above Big Brad's Bar gets up and approaches the balcony's edge twice.
Continuity mistake: When Audra takes lemonade to Will inside the place where he's working as a forger, the pitcher has a liquid which is the true color of lemonade and there's not much left in the pitcher...less than 1/4 of what it could hold. When she comes out of the building, it has the color of iced tea and there's almost half a pitcher of it, which is way more than there should be.
A Horse of Another Color - S2-E21
Continuity mistake: After the Captain and Corporal get out of the cave, they see the Sarge and Jane have ropes on Black Devil. He gets away with their ropes around his neck. He peeks around the rock, and the ropes are suddenly gone. The mare comes after with a rope on her neck that also disappears magically between angles.