There are two rules to live by when placing hidden blocks:
- Do not place the hidden block where hitting it will knock the player into a hole.
- Do not place a block where hitting it will likely knock the player into an enemy.
The first rule is fairly ironclad. The second has a little bit of leeway, so long as the block is at a reasonable height. You can see these rules in play in the hidden block placement in Super Mario Bros.
In World 1-1 of Super Mario Bros., the hidden block is placed where a player is unlikely to find it normally. There is enough room between the hidden block and the hole that a player cannot die by trying to jump over the hole, hitting the block, and falling into the hole.
The secret to Bowser’s World 1-4 castle is that the lower three of the six hidden coin blocks may actually save a player from accidentally jumping into one of Bowser’s flames.
The first hidden block in World 2-1 looks a bit dangerous, but a player is more likely to bounce onto the two green-shelled Koopa Troopas, rather than being knocked into the side of one. Still, it’s possible a player trying to jump over a Koopa Troopa will be pushed back down and will take a hit. This may be why there’s a power-up block before this area, and another one not far after it. (Four power-ups in one level does seem a bit excessive, even for a World 2-1, doesn’t it?)
At the end of World 2-1 is a second hidden block. This one gives the player an easier way up the block tower, rather than having to use the finicky trampoline.
A vine is accessible only by first hitting a hidden block in World 4-2, but if you hit the wrong block, it may be difficult to reveal the vine. This interesting grouping of hidden blocks is safe to hit because there are no enemies in the area.
It doesn’t look like there’s much to say about World 5-2’s hidden block, but its position is actually quite clever. There’s no way Mario can hit the brick blocks jumping from the ground, but a player who tries is rewarded by discovering a hidden block. Using that block to hit the bricks rewards the player further with a vine to a coin bonus area in the sky.
The unusual position of the hidden block in World 6-2 is another clever one. If a player jumps off the pipe below the block containing the vine, the player will both reveal the vine and be knocked into a safe area between pipes. At this point, you don’t want the player to die trying to get to the vine, so when the player goes to hop back on onto the pipe, a hidden block is revealed. This gives a safe and easy way to reach the vine
Hopping off a Koopa Paratroopa is not an easy way to reach a necessary warp pipe in World 8-4. Because this level is a maze that keeps sending the player back when they take a wrong path, players will want to try and reach the warp pipe, and may jump around trying to figure out how to reach it. This is when the hidden block reveals itself.