FreeGameDev

I"m currently working on implementing a new powerup that adds a defensive option, of which there is only one provided by the bubblegum. It is just called "Ghost", intended to function similarly to the Boo powerup found in most of the Mario Kart games. It will:

• Make a kart transparent, like the ghost karts found in ghost replays.
• Allow the kart to drive through other karts, bananas, bubblegum puddles, and other weapons without adverse effects. Driving with the terrain/track remains unaffected by this powerup.
• Still allow gift boxes and nitro cans to be collected, unless this is deemed too powerful.
• Give a visual warning when the powerup effect is about to end.
• Last for 10 seconds, unless the kart is rescued.
• Cause the kart to be pushed out of another kart, if it intersects with one at the time the powerup ends.

Unlike with the bubblegum:

• Weapons will pass right though karts under the ghost effect. For the bowling ball, they will pass through such karts. For the cupcake and plunger, they will not target such karts. For the swatter, it will not hit such karts. For the basketball and anvil, if the kart under the ghost effect is in 1st place, they will target the next kart that isn't under the ghost effect.
• Driving through bananas and bubblegum puddles should not have any effect.
• Collisions with other karts will not occur.
• Nothing will be left behind once the powerup time ends.

Optional sound effects can be implemented during powerup activation and ending. This powerup does not implement the item stealing part which would allow players to get items from other karts, though this can be changed. I don't know about the probability that should be implemented yet, though this powerup idea is considered to be a more powerful version of the bubblegum. Parts of the physics system may need to be rewritten to accommodate this powerup idea.
Icon files are attached below.

Since nobody commented. I will: your suggestion is good. I like it. It's better than some powerups present in the game.

From a gameplay perspective, this idea seems very reasonable. 10 seconds is probably too long, but such a parameter is easy to tweak after playtesting so it's not a concern.

I think the item-stealing part is not needed.

and I don't know when to solve that
What will happen the online mode also there is like the online version 1.0

don't worry, it is for 2.0 in the best case