Party on Midgard!

In an alternate timeline where Loki grows up as a frost giant and not as a prince on Asgard, Thor grows to be a very different prince. When Odin goes into the deep Odin sleep and Frigga travels to another realm to visit her sister, Thor sees this as a great opportunity to invade Midgard… and party! Tracked by Dr. Jane Foster and Darcy Lewis, Thor and his friends across the nine realms arrive in Las Vegas to begin the biggest party Earth has ever seen. Drax, Korg, Nebula, The Grandmaster, and even Frost Giant Loki are only a few of the numerous guests that get invited to go clubbing, see the sights, taste the food, drink the alcohol, and accidentally mess up some of Earth’s most popular monuments. Even Jane and Darcy get in the party spirit when they approach Thor to stop what they thought to be a hostile alien invasion.
The Agents of SHIELD hold different opinions of Thor’s planet wide rave, however. After Director Fury is accidentally hurt when Korg tries to cannonball into a Vegas fountain, Acting Director Maria Hill has zero tolerance for Thor’s shenanigans. Despite a plea from Jane to halt any aggressive action against Thor, Hill calls in the big guns; Captain Marvel. Arriving quickly, she and Thor get into an epic battle across the entire planet as they punch and throw each other across oceans, but Carol Danvers seems to be no match for Thor. According to her, if she were to use her full power she’d leave a giant crater on the planet’s surface. Seeing no other option, Hill sends Captain Marvel back into battle and orders her to not pull her punches. She is about to make her final blow against Thor when Jane enacts her own plan to save Thor and Earth; she calls Thor’s mom.
As Frigga cuts her trip short to visit Earth to scold her son for throwing such a dangerous party, Thor turns to panic. Desperately begging his friends to help, they quickly clean up their mess across the globe so Frigga is none the wiser to their antics. Thankfully, she arrives on a clean Earth and to Thor leading a study group about the various cultures of Earth, even assisted by Captain Marvel herself. Disaster averted, Thor thanks Jane for her help, and to ask her on a date. Things seem to be ending on a happy note, until a portal opens up to an army of Ultrons, led by Ultron inhabiting Vision’s body wearing even more Ultron armor and sporting all six Infinity Stones.
“What If… Thor Were an Only Child?”, or it’s alternative title, “Thor Odinson’s Day Off”, is another one of What If…?’s fun misadventures, similar to T’challa’s adventure as Star-Lord. It’s a simple, yet effective, homage to classic party movies like National Lampoon’s Animal House, Eurotrip, and Superbad. Even the plot can be boiled down to a teenager, Thor, throwing a party, the grumpy adults, SHIELD, want to stop the party, and Thor has to clean up his house, Earth, before his parents come home. There really isn’t much else to say aside from this was just an enjoyable, no stress, fun episode.