Blue Shell

The Blue Shell is a Koopa Shell introduced in Super Mario World. It gives Yoshi the ability to fly. It also turns Mario into Shell Mario. In this form, Mario can perform a shell dash, which allows Mario to defeat enemies such as Thwomps and Boos, but it's very hard to control, and it can cause cheap deaths. It also allows him to swim faster and with more accuracy similar to the Frog Suit, and lets him dodge enemy attacks while crouching similar to the Hammer Suit. It has recently been introduced as an item in Mario Kart: Rise of the Transforming Vehicles, where it acts like a Red Shell, except it freezes its target upon contact.

Koopa Kart: Double Trouble!! (2004)
The Blue Shell is Hammer Bro and Dry Bones's Special Item in Koopa Kart: Double Trouble!!. It can be obtained from 5th to 8th place. When used, it will act like a Red Shell, except it will freeze its target.

Koopa Kart Tour (2020)
The Blue Shell returns in Koopa Kart Tour as Koopa Kid and Larry Koopa's Special Item. It is obtainable from 5th to 8th place, and it serves the same purpose as before.