Pokemon speedruns are nothing new, as you'll likely find hundreds, if not thousands, of people trying to break records in multiple different titles across the franchise. Pokemon Scarlet & Violet is no different, although with the game being essentially brand new, speedrunners are still trying to pin down a meta. Well, it looks like one has been found and involves a Pokemon you're probably not expecting.
Flamigo is a fairly basic Pokemon when you compare it to the rest of the newcomers, but it's turned out to be essential for speedrunning. If you head on over to the Pokemon Scarlet & Violet page on Speedrun.com (thanks Automaton), you'll find that the top three speedrunners so far all utilized Flamigo, including first placed speedrunner truely whose record sits at 5 hours, 27 minutes, and 11 seconds.
A lot of Flamigo's dominance in speedrunning is down to how good its base stats are and how early you can catch it in the game. Flamigo doesn't actually evolve meaning it already has relatively decent physical attack and speed, along with the ability Scrappy that allows Normal and Fighting-Type moves to hits Ghost-Types. That means there aren't many Pokemon out there that can withstand attacks from a Flamigo, making it a pretty powerful team member in the early stages of the game.
With moves like Brave Bird and Close Combat in its arsenal, Flamigo is a force to be reckoned with if you over-level it. Of course, since speed is the goal, most speedrunners will attempt to gather up EXP Candies that are scattered across the map rather than battle trainers and grind against Wild Pokemon. It's yet another way to reduce the time and make sure their Pokemon are powerful enough to quickly take down Gym Leaders, Titan Pokemon, and Team Star.
Another popular choice amongst speedrunners is Hawlucha, another Fighting/Flying-Type that also doesn't evolve - I'm sensing a pattern. Grabbing a Hawlucha takes a bit more time though, meaning Flamigo is the prime candidate if you want to try and rush through Paldea as fast as possible.