In Mario Kart Tour, you will find that sometimes you are just having a hard time passing the person in front of you. As hard as you try, you have been stuck in second place and you're on the last strip of the track with no items at your disposal. Here is where using a technique known as Slipstream comes into play.
Slipstream is the name Mario Kart gives to what amounts to tailgating or drafting, a common feature of racing games. By driving extremely close to a racer ahead of you, you gain a boost which you can then use to pass them. It takes some practice, but once you get the hang of it, you can start winning all your races, even ones which come down to the wire.
To Slipstream, simply drive very close to a driver ahead of you. Keep this close distance for a second or two until you see your muffler exhausting flames and faint semi-circle appears around your character. This indicates your boost is activated and you can now use it to pass the driver. The boost you receive is similar to Mini-Turbo, the blue boost you get with drifting. This technique can be used even if the opponent is bending the corner.
As long as you are not currently in first place, take advantage of this technique. Especially in the section of the race when drivers are bunched together, this is a perfect opportunity to help separate from the crowd.