Difficulty curve
Also said as Challenge curve, Ramp
How hard a game is over time, drawn as a line. A good one starts low and climbs at about the speed the player is getting better.
If the line rises faster than the player, they quit in frustration. If it rises slower, they quit in boredom. Almost every complaint about difficulty is really a complaint about the shape of this line at one point.
Say it
“World 2 is too flat. Enemies should reach full speed by level 2-3, not 2-8. Draw me the curve we have and the one we want.”
Where you’ve seen it
Tetris draws its curve with a single number: as the level rises, pieces fall faster. Slay the Spire lets players bend theirs, with 20 Ascension levels that each add one more difficulty rule.
Not to be confused with learning curve
A difficulty curve is how much the game demands. A learning curve is how fast the player gets better. The art is keeping one just above the other.