Ted Mosby and Marshall Eriksen had an affinity for sci-fi, and the show found unique ways to incorporate common elements of the genre. In total, time travel was presented in three episodes, and even though two of them were tricks, one particular scene confirmed its existence in the How I Met Your Mother universe.
Time travel served as the focus of a season 8 episode appropriately titled "The Time Travelers." While sitting in MacLaren's Pub, Barney invited Ted to Robots vs Wrestlers: Legends, but Ted was reluctant to go. When Barney claimed he would regret the decision 20 years from now, Ted was surprised to encounter twenty-years-from-now Barney. With the help of twenty-years-from-now Ted, the original Ted agreed to go. That changed when other versions of himself, Barney, and a former girlfriend alter his perception.
At first, it seemed as though How I Met Your Mother followed certain rules of time travel that allowed core characters to summon future versions of themselves. Whether it was minutes, hours, or years in the future, Barney showcased every option when it came to time travel. In reality, however, the episode's time travel stemmed from Ted's imagination. He was never invited to go to Robots vs Wrestlers, and instead, planned to go by himself the entire time. Ted only imagined the time travelers to realize all of his friends were too busy for him. Future Ted claimed that if he could go back to that night, he would want to spend the extra days with the "Mother." Even though time travel was used as a storytelling device in season 8, a previous season made it a point to confirm the concept.
How Time Travel Was Confirmed In How I Met Your Mother
Time travel was first introduced in How I Met Your Mother season 4 through "Intervention." The episode began with an older version of Barney claiming his younger self won't be able to solve global warming unless he gets women to sleep with him. This, of course, was just normal Barney in old man makeup, preying on young women with an elaborate ploy to win them over. Despite the prank, time travel was confirmed in the very next season with the episode titled "The Window."
Marshall received a box of childhood belongings when he finds a letter from 1993 written to his future self. It primarily insisted that discover the Loch Ness Monster, so if anyone excelled at time travel in the series, it would be him.