Demo 7.5, also known as Cheep Demo, is the second latest demo to be officially released to the public, the latest being the 1-1 Demo. It's an ASM demo featuring several new Star and Special Zone levels, a few random redone levels and custom music. It's the prequel to the Overworld Demo and the sequel to the Demo 7.
In the demo, Mario starts in a submap with the levels that have been redone or created, every single one of them is available from the start. Every level appears in the next demo, some replacing existing levels.
Every demo after this one is either unofficial or just some leaked levels, with almost none of the levels working right due to the removed sprites.
When you beat some levels, the events that should happen in the Demo 7's Special Zone can graphically glitch the submap you're in, but you cannot get stuck.