Why difficulty is the hard part of casual puzzles
The difficulty curve is probably the single most important design decision in any puzzle game. Too steep and the player quits in frustration at level 8 and uninstalls. Too flat and they get bored by level 20 because it feels like they have already seen everything.
When I started designing Royal Chest, I had 48 levels ahead of me and a question that kept me up at night: how do I make sure a 9-year-old can enjoy the opening stretch without an experienced adult finding those levels insultingly easy?
The answer I landed on was to split the experience into four clearly distinct phases, each with its own internal mini-curve. That was not my first idea. I tried three different approaches before I got there. The first was linear (each level a little harder than the last) and it felt monotonous. The second was randomized and produced impossible difficulty spikes. The third — the four-phase structure — was the one that worked.
The four phases of our curve
| Phase | Levels | Mechanics | Goal | Estimated time |
|---|---|---|---|---|
| Introduction | 1–12 | One chest, simple matches | Teach the basic rules | 20–30 minutes |
| Coordination | 13–24 | Two chests, combo chains | Combine mechanics | 30–45 minutes |
| Strategy | 25–36 | Three chests, timed pieces | Plan ahead | 45–60 minutes |
| Mastery | 37–48 | All mechanics combined | Full command | 60–90 minutes |
Phase 1 (levels 1–12): Introduction
The first twelve levels are basically a tutorial in disguise. Level 1 has a single golden chest in the center of the board and three jewels of the same color around it. The player only has to drag one jewel into the chest to complete the match. It is almost impossible to fail.
From level 2 through 6, I add one more jewel per level and rotate the colors. The player learns that colors matter, that matches of four score more, and that matches of five trigger a special effect. None of this is spelled out in text. The game simply shows it through increasingly elaborate animations as the matches grow.
Levels 7 through 12 introduce basic obstacles: stone blocks that cannot move, walls that limit the available moves. This is where the player starts thinking strategically, even though the difficulty is still low.
Phase 2 (levels 13–24): Coordination
Level 13 brings in the second chest. That changes everything. Now the player has to manage two chests at once and decide which one to feed first. Jewels that are not going into one chest can still serve the other, so every move does double duty.
This phase also introduces combo chains: when you clear pieces next to other matches, they trigger cascading reactions. Levels 18 through 22 are built specifically so the player discovers they can plan multi-hit combos. Level 20 is my favorite in this stretch — it has a layout where one well-thought-out move clears 70% of the board.
Phase 3 (levels 25–36): Strategy
The third chest appears at level 25 and, on top of that, timed pieces enter the mix. Some jewels carry a counter that ticks down with every move. If you do not clear them before it hits zero, the level ends.
This is the phase where the game stops feeling casual and starts demanding planning. Levels 30 through 34 were the ones that took me the longest to design. Level 32 in particular went through seven rewrites. The early versions were too easy. The middle ones were impossible. The final version requires exactly three correct opening moves to unlock the rest of the board.
Phase 4 (levels 37–48): Mastery
Here it all comes together. Three chests, timers, obstacles, combo chains, and a few new mechanics that only show up in this phase — such as armored chests that need two adjacent matches to open.
The last three levels (46, 47, and 48) are designed as a real challenge. Level 48, the final stage of the game, combines every mechanic on a large board and takes between 15 and 25 minutes to clear. I wanted it to feel like a worthy "final boss": hard, but never unfair.
The "click moment": when it all locks in
During development I noticed something interesting. There is a point in each phase where the player shifts from learning to mastering. I call it the "click moment." It is that one level where everything suddenly makes sense and the player realizes they can solve situations that felt impossible five levels earlier.
In Phase 1, the click moment lands around level 9, when the player is moving pieces fluidly and has stopped consciously thinking about every move. In Phase 2, it is level 19, where combo chains start to feel natural. In Phase 3, level 31. And in Phase 4, level 43.
Those levels get extra care. They are slightly easier than the ones around them, because they work as "cognitive rest stops" where the player consolidates what they have learned before facing the next difficulty spike.
Playtesting: what 12 people taught us
Before launch, I had 12 people play the game: friends, family, a couple of fellow developers, and a few strangers I recruited at a café in Fort Worth. Sessions ran from 40 minutes to two hours, depending on how far each person got.
The results were eye-opening. For example, the original level 15 was 40% harder than I thought. Seven of the twelve people got stuck there. I simplified it by moving two pieces and the problem disappeared.
Another interesting data point: age did not correlate with progress speed. A 62-year-old woman reached level 35 in her first session, while a 28-year-old programmer stalled at 22. The difference seemed to come down more to patience and a willingness to experiment than to age or gaming experience.
The person who got the farthest was a 14-year-old who cleared all 48 levels across three one-hour sessions. They told me level 47 felt "a little silly" because it required too much luck. They were right — I adjusted the piece layout to cut down the randomness and the level got much better.
Ultimately, playtesting taught me that designing levels is only half the job. The other half is watching how real people interact with them and having the humility to change what does not work, no matter how much you like the original design.