The story starts with Sonic and friends trying to defeat Dr. Robotnik and take back the Chaos Emeralds. In another universe, Mario and Luigi are rescuing Princess Peach from Bowser. Something causes the Power Stars and Chaos Emeralds to combine, leading to Sonic and Mario being stuck in each other's worlds. The two have to figure out how to work around their contrasting gameplay styles and get back home.
The project began in 2008 when the creator, Liam Doherty, was still in high school. Unsatisfied with the original short, he tweaked it for several years until he finally uploaded it to YouTube in 2015.
Mario & Sonic: Worlds Clash provides examples of:
- Another Dimension: Sonic's World and the Mushroom Kingdom are in alternate dimensions.
- Big Bad Ensemble: Bowser and Dr. Robotnik, of course, serve as the Big Bad of their respective worlds.
- Big Damn Heroes:When it seems like Dr. Robotnik has Mario and Tails beat, thanks to having Metal Sonic on his side, Knuckles (who had wandered off on his own earlier) bursts in to even the playing field.
- Brick Joke: While in Mario's world, Luigi gives Sonic a mushroom to make him grow, much to the latter's shock. At the end, Sonic pulls out another one and grows larger again, leaving his friends speechless.
- Crossover: Between Super Mario Bros. and Sonic the Hedgehog.
- The Dragon: Metal Sonic serves as this to Dr. Robotnik, of course.
- Drop the Hammer: Mario makes use of his during the final showdown with Dr. Robotnik.
- Eleventh Hour Super Power: The Chaos Emeralds and the Power Stars, on top of granting Mario and Sonic the ability to travel back to their respective home dimensions, also give Mario his super cape and turn Sonic into Super Sonic, so they can wrap things up with Dr. Robotnik and Bowser.
- Shout-Out: After Mario gets sucked into the portal to Sonic's world, Luigi repeatedly calls out "Mario?" towards the portal, like he does when trying to find his brother in Luigi's Mansion.
- Spiritual Successor: The short takes inspiration from Super Mario Bros. Z.
- Took a Level in Badass: Mario initially has trouble keeping pace with the other characters in Sonic's world, but eventually gets the hang of it.