Another idea for a kart:
The Kart Marine
err Speed Kart Submarine, handles under water better than any other kart.
It shouldn't have any propellers just water thrusters or something
Jetboat Kart
Like the Boat Kart except its faster, uses water thrusters like the Kart Marine.
And for Items:
Barrier/Shield (A shield the color of your Kart Spawns and protects you for a while or until you are hit.)
Giant Purple/Blue Homing Missile( It heads for the kart that is in first somehow)
Oil Can (Drops a Blob of oil behind your kart, causes others to spin out)
Ink Balloon(If you hit an enemy with it they have and ink splot like the Blooper in Mario Kart)