From 100 to 200 levels: rolling out a difficulty curve across 9 worlds

The starting point: 6 worlds, 100 levels, 6 colours

At first release, the Huevo campaign consisted of 100 levels across six worlds — The Nest, Coral Garden, Tidal Pools, Sunset Ridge, Aurora Cave and Rainbow Peak — with a palette of six ball colours. Enough for a first impression, not enough for long-term retention. Players who finished the campaign had nowhere to go except Endless Mode.

Three new worlds, a 10-colour palette

The expansion added three new worlds — Crystal Depths (9-colour), Starfall Summit (10-colour) and Infinity (8-colour mastery) — and extended the palette with BallLime and BallBrown starting at level 101. The 10-colour palette is more than cosmetic: at nine or ten colours simultaneously, sorting becomes a fundamentally different cognitive problem than at six. Working memory is taxed harder, pattern recognition slows down, and difficulty rises without adding a single tube.

Visual cohesion for the late game

The late-game worlds share their own visual language. Crystal Depths, Starfall Summit and Infinity all use a "cavern frame" silhouette — a shared edge shape that ties the three worlds together without making them identical. Crystal Depths is a bioluminescent underwater cavern, Starfall Summit a mountain summit during a meteor shower, Infinity a cosmic void with nebula swirls. Before the dedicated backgrounds landed, Huevo fell back to Rainbow Peak with an accent tint — workable but lazy. With the new backgrounds, the last 100 levels signal "this is a different part of the game".

The curve: not "harder", but "differently heavy"

A common pitfall in level expansions is to scale difficulty linearly. More colours, more balls, more tubes, done fast. For Huevo the choice was deliberate to revise the curve: at level 101 the palette widens to seven colours, at 121 to eight, at 161 to nine, and at Starfall Summit to ten. In between, balls-per-tube and the number of empty tubes alternate so no two consecutive levels share the same "shape". That is not coincidence but the result of a bracket curve that lives explicitly as a data structure in the level definitions.

Tooling that makes the curve possible

The expansion provided a natural reason to professionalise level tooling. World transitions, narrative strings in EN+NL, a star-chase system showing "X moves away from 3 stars" hints on the win screen after sub-three-star replays — none of these are visible to a player who only plays levels, but they are the reason 200 levels stay maintainable for a small indie studio. What is invisible in a single level is, across 200 levels, the difference between a series and a mishmash.