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Rule 1: Do not use random behavior in traps and enemies.

Also it's assumed you already have an idea for a level design.

Rule 1: Do not use random behavior in traps and enemies. This is why Roguelikes could be problematic if they are not fine tuned as randomness could create massive difficulty spikes if not handled correctly.

Also it's assumed you already have an idea for a level design.

Racers

Racers are surprisingly simple to tweak. You play the game and get the playtesters best times. Now you simply make the enemies drive nearly as fast as that. You could make them a slightly slower ghost version of the best player or alternatively, make them faster but allow the player to slow them down using weapons, collisions and what not.

You could also record the player's car behavior and path during the run i.e break, accelerate, turn right and left and then construct a course based on that path. Placing oil spills, rocks and other obstacles on the road that would likely lead to a loss (similar to platformers).

General

It does not matter what game you are making, record the winning key strokes, add an epsilon room for mistake and let the player lose otherwise. It could be DDR, endless runner and what not in this case. The idea is to visualize the obstacles in a compelling way instead of making an invisible wall of death or something that confuses the player. You need to let the player understand why they are losing over an over or they would quickly rage quit and for a good reason.

tl;dr Make the level unpassable and then trim traps and bullets/projectile' timings that no test player was able to avoid. Keep the ones the test players managed to avoid. You can draw statistics on how many times a certain trap was avoided to measure it's difficulty level. Also to increase or lower difficulty, you can make a trap that normally does damage insta-kill the player instead and vice versa.

The actual way this is done by professionals is simple.

1. Add all the possible traps, turrets, spikes and flaming balls of lava you can think of to an excess into the room you wish to make difficult.
2. Make them run automatically on a timer (so the behavior repeats itself) or as response to player movement (i.e the lava ball spawns when the player approached).
3. Pay the level once while doing your best and avoiding as many collisions with death-traps as possible (you could also let a very skilled alpha-tester play instead).
4. Have the game code record every collision between your character and a death trap. Remove these traps or attempt the level again and avoid more of the traps.
5. To make this easier, you could slow down the game without changing it's rules and behavior.

There is no other true way to maximize difficulty. You need to make it so only one tiny route is passable without dying. To make it easier, increase the bounding box of the character responsible for removing death traps during testing.

Just to be clear, when I say remove I mean that if the lava pit spawns 10 lava balls per 15 seconds and your test character touches two of them, remove only the two spawns from the timed spawner. If you can't avoid a specific spike that is there 100% of the time, you remove it completely. The same principle regarding the lava balls applies to turrets as well.

Also it's assumed you already have an idea for a level design.

Rule 1: Do not use random behavior in traps and enemies.

The point is only making the game hard to beat; this may sound obvious but you also need to convey to the player what challenge they are facing and why they failed, otherwise it would be just one of those trial and error "trapformer" games.

Platformers

tl;dr

1. Make the level completely unpassable.
2. Then slowly trim traps and bullets/projectile' timings that no test players were able to beat. Keep the traps that the test players managed to avoid. You can draw statistics on how many times a certain trap was avoided to measure it's approximate difficulty level.
3. To increase or lower difficulty dramatically, you can make a trap that normally does damage insta-kill the player instead and vice versa.

longish version:

1. Throw in all the possible traps, turrets, spikes and flaming balls of lava you can think of to an excess into the room you wish to make extremely difficult.
2. Make them run automatically on a timer (so the behavior repeats itself) or make them activate as a response to player movement (i.e the lava ball spawns when the player approached). The point here is do not use random behavior as it is extremely hard to test.
3. Play the level over and over while doing your best and avoiding as many collisions with death-traps as possible (you could also let a very skilled alpha-tester play instead).
4. Have the game code record every collision between your character and a death trap. Remove the traps you were never able to avoid in any of your attempts.
5. To make this easier, you could slow down the game without changing it's rules, physics and behavior. This will let you simulate the playing skills of a player with extremely fast reflexes and lots of patience.
6. You could increase the size of the bounding box of the collidable test character to make things a bit easier for the real players.
7. Record you winning play through and systematically add obsticles that would have been avoided during your victorious run.

Just to be clear, when I say remove I mean that if the lava pit spawns 20 lava balls per 5 seconds and your test character touches two of them, remove these two spawns from the timed spawner. If you can't avoid a specific spike that is there 100% of the time, you could remove it completely or turned it into a timed trap that is active only 50% of the time (like an electrical barrier, a flamethrower or a laser). The same principle regarding the lava balls applies to turrets as well.

Also it's assumed you already have an idea for a level design.

tl;dr Make the level unpassable and then trim traps and bullets/projectile' timings that no test player was able to avoid. Keep the ones the test players managed to avoid. You can draw statistics on how many times a certain trap was avoided to measure it's difficulty level. Also to increase or lower difficulty, you can make a trap that normally does damage insta-kill the player or the opposite.

The actual way this is done by professionals is simple.

1. Add all the possible traps, turrets, spikes and flaming balls of lava you can think of to an excess into the room you wish to make difficult.
2. Make them run automatically on a timer (so the behavior repeats itself) or as response to player movement (i.e the lava ball spawns when the player approached).
3. Pay the level once while doing your best and avoiding as many collisions with death-traps as possible (you could also let a very skilled alpha-tester play instead).
4. Have the game code record every collision between your character and a death trap. Remove these traps or attempt the level again and avoid more of the traps.
5. To make this easier, you could slow down the game without changing it's rules and behavior.

There is no other true way to maximize difficulty. You need to make it so only one tiny route is passable without dying. To make it easier, increase the bounding box of the character responsible for removing death traps during testing.

Just to be clear, when I say remove I mean that if the lava pit spawns 10 lava balls per 15 seconds and your test character touches two of them, remove only the two spawns from the timed spawner. If you can't avoid a specific spike that is there 100% of the time, you remove it completely. The same principle regarding the lava balls applies to turrets as well.

Also it's assumed you already have an idea for a level design.

tl;dr Make the level unpassable and then trim traps and bullets/projectile' timings that no test player was able to avoid. Keep the ones the test players managed to avoid. You can draw statistics on how many times a certain trap was avoided to measure it's difficulty level. Also to increase or lower difficulty, you can make a trap that normally does damage insta-kill the player instead and vice versa.

The actual way this is done by professionals is simple.

1. Add all the possible traps, turrets, spikes and flaming balls of lava you can think of to an excess into the room you wish to make difficult.
2. Make them run automatically on a timer (so the behavior repeats itself) or as response to player movement (i.e the lava ball spawns when the player approached).
3. Pay the level once while doing your best and avoiding as many collisions with death-traps as possible (you could also let a very skilled alpha-tester play instead).
4. Have the game code record every collision between your character and a death trap. Remove these traps or attempt the level again and avoid more of the traps.
5. To make this easier, you could slow down the game without changing it's rules and behavior.

There is no other true way to maximize difficulty. You need to make it so only one tiny route is passable without dying. To make it easier, increase the bounding box of the character responsible for removing death traps during testing.

Just to be clear, when I say remove I mean that if the lava pit spawns 10 lava balls per 15 seconds and your test character touches two of them, remove only the two spawns from the timed spawner. If you can't avoid a specific spike that is there 100% of the time, you remove it completely. The same principle regarding the lava balls applies to turrets as well.

Also it's assumed you already have an idea for a level design.