Floating pipes first appeared in Super Mario Bros., in World 5-1 and World 6-2. These appearances set the initial foundation for a floating pipe. The Lost Levels further defined their use. Following the rules set by these games will improve the appearance of floating (and hanging) pipes in levels designed using Super Mario Bros. mode.
The most important design detail for a floating pipe is that the opposite end must never be left open.
Options for handling the a floating pipe differ slightly depending on whether the pipe is upright, or upside-down.
Upright Floating Pipes
The design of the pipe requires it be against something. In Super Mario Bros., this was done by placing unbreakable blocks against it.
It’s important that the blocks be unbreakable. If they can be broken, then you are left with the incomplete appearance.
Another design choice is to place ?-blocks underneath a floating pipe, as seen in The Lost Levels World 1-1.
As a general rule, you want to leave three tiles of space between the blocks and the ground. This gives Super Mario enough room to comfortably run and jump underneath it.
There are always exceptions, such the first floating pipe in Super Mario Bros. World 6-2. The pipe here leaves four tiles of space underneath, due to the placement of ground pipes immediately after it.
Exceptions only exist when a well-designed level requires it. Randomly placing a pipe higher or lower without thought to its placement is not an exception to the rule.
Upside-Down Floating Pipes
The Lost Levels added upside-down floating pipes in World 5-1. These followed the same style of using blocks over the opposite end.
However, as seen in the underground 5-2 and the aboveground 7-1, upside-down pipes can be attached to the breakable bricks. This is allowed because the pipes prevent Mario from breaking the bricks. However, this style should not be used if the stage makes use of the P-Switch, which turns brick blocks into coins.
In The Lost Levels World C-1, ?-blocks even appeared at the top of an upside-down floating pipe, although the player is unable to get the coins from these blocks.
Double-pipes appeared only once in the first two Super Mario games. In the Lost Levels World D-2, two pipes are joined by blocks.
An alternate design choice, which did not appear in the first two Super Mario titles, is to join two pipes without blocks.
This design suggests the pipe can float without blocks to hold on to. This concept was first hinted at in Super Mario Bros. 3 World 4-1 with pipes inside a waterfall, and later appeared in many World 7 levels.
Super Mario Bros. 3 World 8-1 used blocks between two pipes, perhaps because the upper pipe is a warp pipe. This would show that going down the top of the pipe will not lead Mario out the bottom of the pipe in the same area. This is an important point: if either end of the double-pipe is a warp pipe, place blocks between the two pipes to show they are not completely connected.
The final design appearing in the first two Super Mario titles only appeared once, in The Lost Levels World A-1. An upside-down pipe reached the edge of the screen, giving the illusion that it continued beyond the player’s view.
Super Mario Maker allows you to design Super Mario Bros. levels beyond what appeared in the original two Super Mario titles. Keep in mind the reasons behind the design decisions in these earlier titles, as well as your observations in later titles, when designing levels in the Super Mario Bros. style. A little bit of design thought goes a long way to create a level that feels right.