How to introduce game rules gradually without breaking earlier levels?

Question

In particular, suppose I introduce a new rule in level 10 but the player decides to replay some earlier levels. The new rule doesn't apply to to them but the player may have forgotten that.And so it would not be clear which rules are active when replaying earlier levels.Is there a good solution to this problem?

LanternLight83 · Accepted Answer

Most rules are tied to particular elements of play, and in most games, the involvement of a specific rule is indicated by association with a color which can applied as an accent to those elements. You can tell when en passant applies in chess because potential moves are clearly indicated, when poison is involved because the enemies, terrain, or even just the screen-vignette is tinted green. If you can integrate a color into the entities that are most directly affected by the rule in later situations, then players can infer the rules absence by the absence of the color indicator, which should stand out enough to be notable but be subtle enough to still look cohesive in later levels.

Someone · Answer

A good solution is to make it impossible to use the more complex rules. For example:
- don’t put pawns or rooks in the first levels of chess, so that players won’t try to take en passant or to castle.
- only put cars with automatic gear boxes in the first levels of a racing game, so that players won’t try to switch gears manually.
- don’t have under water/vacuum spaces/mountains/swamps or more advanced enemies or weapons in the first levels of a first person shooter.
That may not work for every game, though.
You can also make the UI visually distinctive in the earlier levels. Less detailed images may help cue the user that they have fewer/simpler features.