Dynamic Difficulty Adjustment

The Dynamic Difficulty Adjustment (DDA) is a system introduced in Crash Bandicoot 2: Cortex Strikes Back and then also implemented in many later Crash Bandicoot platforming games, designed to help players struggling with a certain level or section of a level. The idea was to make the game easier for players who were struggling, without making the game easier for better players who would like a more challenging game. The DDA was thoroughly planned out by Naughty Dog in Crash Bandicoot 2: Cortex Strikes Back and Crash Bandicoot: Warped, but a very minimal version of it is included by later developers in Crash Bandicoot: The Wrath of Cortex, Crash Bandicoot: The Huge Adventure, Crash Bandicoot 2: N-Tranced and Crash Bandicoot 4: It's About Time.

Jason Rubin described the reasoning behind the DDA as comments included in a 2011 blog article by fellow Naughty Dog co-founder Andy Gavin describing the improvements made after the first Crash Bandicoot game. The quote below by Rubin is taken from that article.

"We were already learning. We had realized that if a novice player died a lot of times, we could give them an Aku Aku at the start of a round and they had a better chance to progress. And we figured out that if you died a lot when running from the boulder, we could just slow the boulder down a little each time.  If you died too much a fruit crate would suddenly become a continue point. Eventually everyone succeeded at Crash.

Our mantra became help weaker players without changing the game for the better players.

''We called all this DDA, Dynamic Difficulty Adjustment, and at the time the extent to which we did it was pretty novel. It would lead later Crash games to be the inclusive, perfectly balanced games they became. Good player, bad player, everyone loved Crash games. They never realized it is because they were all playing a slightly different game, balanced for their specific needs.''"

Crash Bandicoot 2: Cortex Strikes Back
If the player dies repeatedly in a certain section of a level, then after about 5 or 6 deaths, Crash will be given an Aku Aku mask (or a ? crate will become an Aku Aku one like in the level Spaced Out due to its proximity to a checkpoint), and will continue to on subsequent deaths until reaching the next checkpoint. Also, there are certain ? crates in various levels that are programmed to become checkpoint crates after about 12 deaths. Here are some more details about the DDA in this game.
 * In chase levels, if the player continually dies, the boulder or bear will start to move slower. Since Aku Aku is banned from those levels and it doesn't make sense to have a checkpoint in the middle of a chase, this was a different way of providing help in those levels.
 * The game remembers the deaths encountered in sections of the level during saving the game. If the player has had a lot of trouble in a certain section, the new checkpoints that appeared will remain there in the saved game.  Similarly, if the player has triggered an Aku Aku appearing at the beginning of a level, Crash will be awarded an Aku Aku upon entering the level every time from then on (unless he enters the level with 2 masks, then he won't be given invincibility).  Similarly, if the player has triggered an Aku Aku appearing at a certain checkpoint, it will happen from then on any time Crash dies and returns to that checkpoint.
 * Furthermore, the saved data includes memory on how much the player has died in sections of the levels, so sometimes even if the player hasn't triggered Aku Aku/extra checkpoints appearing on the save file, it might sometimes occur after dying once or twice if the player has died a lot there before.
 * If Crash is awarded Aku Aku at the beginning of the level, then it will trigger the game on subsequent entrances to the level to give Crash the Aku Aku mask, even if it's a different entrance.  For example, if Crash died a lot in the Snow Go secret area leading to the red gem, then because of that, if Crash enters Snow Go the normal way, Crash is awarded an Aku Aku mask, since the game remembers he was given Aku Aku at an entrance to the level.
 * If Crash skips a checkpoint, then the subsequent "help checkpoints" will be in their ? form.
 * In special paths, it's never possible for a crate to turn into a checkpoint, but being awarded Aku Aku is possible. Special paths are paths that are not part of the main path of the level, and include death routes, gem paths, secret entrances, as well as many other paths such as the underground areas of Turtle Woods and Un-Bearable.
 * When the player has tricked the game into thinking Crash is in a bonus round by using the bonus glitch, then the "help checkpoints" will be in their ? form.

Crash Bandicoot: Warped
The DDA works exactly like it did in Crash Bandicoot 2, except that in the NTSC-U version, Crash (or Coco) can additionally be awarded 2 Aku Aku masks by continuing to die repeatedly after being awarded one Aku Aku mask. This is not the case, however, in the PAL version.

Crash Bandicoot: The Wrath of Cortex, Crash Bandicoot: The Huge Adventure and Crash Bandicoot 2: N-Tranced
In these games, Crash or Coco can be awarded a single Aku Aku mask upon repeated dying at the beginning of a level or at a certain checkpoint. This is the full extent of the DDA in these games. No data of past trouble is saved in these games, so Crash or Coco will never be awarded an Aku Aku mask upon entering a level, even if the player died a lot there in the past.

Crash Bandicoot N. Sane Trilogy
The same DDA from Crash Bandicoot: Warped's NTSC-U returns in the N. Sane Trilogy, with an Aku Aku mask being granted at 7+ deaths, some crates becoming Checkpoint or Aku Aku crates at 12+ deaths, and finally a gold Aku Aku mask at 14+ deaths.