During the development of Halo: Combat Evolved, Master Chief was originally going to be called "Commando." He was renamed "Master Chief" as a placeholder name, but the name stuck.
In a trailer for Halo: Combat Evolved, a Covenant Elite was shown wielding an Energy Sword and a shield! Later on in development, the shield was taken off the Elites and given to the Jackals.
There were tablet computers invented before the iPad popularized the device.
During the original release of the anime adaptation of Dragon Ball Z, Vegeta's first appearance saw him in a different color scheme than what we're used to. However, by the time he arrives on Earth in the events of the show, his color scheme is apparently corrected. If I remember correctly, this color confusion was because Vegeta's true color scheme wasn't decided on by the time his first anime appearance was made. The manga chapter in which he first appeared was released in black-and-white, so the animators invented a color scheme for Vegeta and his comrade Nappa and used those colors until a final palette was decided on. However, in Dragon Ball Z Kai, Vegeta's color scheme was corrected to what we're used to.
Similarly, when the movie Dragon Ball Z: The Tree of Might was advertised to premiere at an anime fair, there was a poster made for the occasion. On the poster, the movie's main villain Turles is shown with a color scheme that ended up being different from how he looked in the movie, which was most likely completed by the time the poster was made.
The cartoon show Danny Phantom would have gone on longer had it not been cancelled by Nickelodeon. The creator Butch Hartman stated that a fourth season would have involved a rematch with Danny's ultimate enemy, an adult version of himself from a bad timeline, who he fought in the second season.
Stephen Christian, a singer-songwriter and former lead singer of the now-disbanded Anberlin, stated that he once beat Super Mario Bros. Given his age, it's safe to assume that he meant the one on the NES.
The infamous Dragon Ball GT has 65 episodes, the first 17 of which were "lost episodes." Those 17 episodes were so hated and so different from what Dragon Ball Z fans were used to, that in a series re-release, the first 17 episodes were cut out and footage from them was turned into a special episode made for the re-release. Due to the big skip to the better stuff, this made the series shorter and a little more akin to the liking of longtime Dragon Ball fans.
Selfies were a thing long before social media popularized them.
When the video game Mighty No. 9 was released, it was so poorly-received, that Sonic the Hedgehog made fun of the release on his twitter! Let's get one thing straight; if Sonic can get away with dunking on a game release and people near-unanimously agree with him, the game's that bad.
When Charles Schulz was making A Charlie Brown Christmas, CBS executives urged him to include a laugh track in the special. Schulz refused, stating that he wanted fans to enjoy the special at their own pace and not be told when to laugh. Sure enough, he stayed true to his word and didn't even try to put a laufgh track in. CBS was afraid that the special would flop, but released it anyway. The special was a hit and became a holiday favorite, ensuring that there would never be a laugh track in future specials. Meanwhile, CBS actually created a version of the special with a laugh track, but the version is unavailable for viewing.