Clyde Bruckman's Final Repose - S3-E4
Character mistake: Clyde Bruckman says that the Big Bopper won a coin toss that put him on the plane that crashed and killed him along with Buddy Holly and Ritchie Valens. The person who actually won the coin toss was Ritchie Valens.
The Way of the Warrior (2) - S4-E2
Character mistake: During the Defiant's flight to save the Cardassian officials, Worf says something to the effect of, "I've never been aboard a Federation ship equipped with a cloak before". However, he was aboard the Enterprise during the Pegasus incident, where The Ship was temporarily equipped with a cloaking device.
Character mistake: Zordon begins to explain to the Rangers about their powers and then their Zords. At one point, he says "You need only to turn to the power of your Dino Zords." However, the subtitles get it wrong and spell it as if he's saying "Dinosaurs" instead of Dino Zords which is what he says. (00:10:38)