Hol up

But isn't Wario fourth?

Luigi's 4th, Wario is 6th, but his place doesn't matter since the blue shell will hit whoever is in 1st when it's launched

But what does the blue shell do?

It's a race, when the blue shell hits 1st place, it explodes and temporarily immobilises them allowing other racers a chance to get to first. This guy is in 1st but then sees that someone has a blue shell, so he moves to 2nd so he wont get hit and can pass whatever poor sop is in 1st after they get hit with the blue shell.

Thank you