They see him rollin'...
The El King is Squilliam Fancyson's shopping kart. It is a shopping kart that has been upgraded with turbo-boosts, missiles, solid gold shields, and has a unibrow on the front of it. It is also copyrighted by Squilliam, so reading this page is now illegal, you know.
The El King can be unlocked in the shame Mario Mart by completing the whole demolition mode with Giygas. However, Chuckles the Cheat and Sarah Palin got together one day to play Mario Mart, and discovered that if you just tell your copy of Mario Mart that you already beat demolition mode with Giygas, it will give it to you anyways.
It is designed like a limousine and it can house one person.