That's a wheel in place of a chest on Koraidon (Scarlet) and what looks like a motorcycle seat on Miraidon's (Violet) back. They're... bikes?
These flags remind me of racing flags too, and Pokémon Centers that look like gas stations...
Today I got to witness @pChalTV beat #Pokémon #emeraldkaizo on his 151st run and it brought on a whole new level of existential meltdown. Big congrats, Jan! Your hard work and dedication this year are unparalleled.