The standard position for blocks is to leave three empty rows between the blocks and the ground, or another set of blocks, beneath. There are times when blocks may be placed higher or lower, but these are the exception to the rule.
The Rule of Block Heights
The beginning of Super Mario Bros. World 1-1 introduces to what is essentially the rule of block height. Blocks appear on the fourth and eighth rows above the ground. By following this rule, your levels will always give the player enough breathing room to move around, while a nostalgic feel for the design of the other Super Mario Bros. title.
At this height, Super Mario can comfortably fit underneath the floating blocks. If the blocks are lower, Mario will more easily hit an oncoming enemy, with no room to maneuver. When blocks are above blocks, even if there are no enemies, leaving three empty rows keeps the spacing from feeling claustrophobic.
The spacing rule is typically followed for higher blocks even when there are no lower blocks beneath, especially when there are lower block very nearby. This is seen in World 2-1, where the upper blocks are essentially beyond Mario’s reach without first jumping off of an enemy, such as a hopping green-shelled Koopa Paratroopa.
Exceptions of the Block Height Rule
Once a rule has been established, the first thing to consider is when (and why) that rule should be broken. There are plenty of situations when placing blocks higher or lower than the common locations is beneficial. It is important to understand why these uncommon placements are used, and any caveats to that placement.
An early exception to this rule is at the start of World 3-1. Here, a couple of ? blocks are raised by one square, leaving four squares beneath them. These higher blocks have a significant difference in their placement. While the lower blocks can be reached by simply pressing the jump button, these higher blocks cannot be hit by pressing the jump button. Instead, the player must press and hold the jump button. Of course, holding the jump button is a skill that any player would learn in World 1-1, simply by necessity to get past the first set of pipes.
Later in World 3-1, two rows of block are squeezed together by raising the lower set of blocks. This is purposely done to make it more difficult for the player to get into the blocks, where a vine leads to a coin bonus area.
A longer jump in World 5-2 is made a little easier by moving a set of blocks up one row. If these blocks were at their standard height, Mario would be more likely to hit the blocks when jumping, causing him to fall into the hole.
Another area in World 5-2 leaves only a single row underneath blocks containing ten coins and a power-up. Although Super Mario can reach these blocks with a run-duck-slide technique to grab a Fire Flower, this area is clearly intended for players who reached this area as small Mario to get a Super Mushroom. This level is rare in that it gives another power-up just a screen and a half later, likely the intended spot for players who were already Super Mario to get a Fire Flower. This effort to get the player through with fire power is likely because World 5-3 contains only one power-up, followed by a short by difficult castle, which also contains only one power-up.
The Lost Levels uses a non-standard height to make an invisible block more difficult to find. Players moving fast enough may hit the block after bouncing off of the red-shelled Koopa Troopa beneath it, but otherwise the player is left to choose between trying to cross a jump that is clearly too far, or blindly jumping. Just pressing the jump button isn’t enough, as the button needs to be held for Mario to get enough height to reach the invisible block.
This situation is intended for more skilled players. A more skilled player will understand immediately that they cannot cross the hole in a jump unless they jump from the pipe on the floating blocks. Such a player will determine that there must be a hidden block they can reveal to reach the pipe. Even then, having a hidden block here is only acceptable to the player because there is a small area to search. The wider the area where a hidden block may be, the more time and effort it takes the player to find it, and the less enjoyable that section of the level will be for the player.
In The Lost Levels World 4-1, there is a claustrophobic area of ? blocks. The key point to this area is that there are no enemies underneath. If there were enemies underneath the blocks, there would be too much risk of the player being unable to avoid one.
The opposite situation appears later in World 4-1, where blocks are placed one row higher than usual. A pipe leading to an underwater bonus area is accessible only by jumping onto a couple of these higher blocks. This extra difficulty to reach the pipes will discourage some players from trying, but it rewards those who take on the challenge.
A tight spot at the start of World 4-2 holds a power-up in a block one row lower than usual. This is due to the placement of the Bullet Bill canons, to create a difficult-to-reach power-up.