A physics-based sphere game across multiple levels: navigating crystal cave mazes, dodging projectiles, and collecting crystals — taught step by step.
This project is a physics-based game prototype built entirely in Blueprints with Unreal Engine 4, set across multiple crystal cave levels. The player controls a sphere that must navigate mazes, avoid incoming projectiles, and collect crystals to progress. Like the Endless Runner, it was built without following a specific course. The development process was recorded in a full teaching playlist.
You can watch the complete teaching playlist here: YouTube Playlist
You can also watch a demo here: YouTube
Physics Sphere as the Player Character
Like the Marble Run project, the player character is a physics-simulated sphere driven by AddForce and AddTorque rather than UCharacterMovementComponent. The sphere rolls through the environment responding to gravity, friction, and surface geometry — the player influences the simulation rather than controlling the character directly.
The Crystal Cavern extends the Marble Run’s pure rolling mechanic with additional gameplay layers: mazes to navigate, projectiles to dodge, and crystals to collect. Each of these adds a distinct design dimension on top of the core physics movement. The maze introduces spatial navigation and dead-end decision making. The projectiles introduce threat and reaction timing. The crystals introduce a collection goal that motivates thorough exploration of each level.
Maze Design for a Rolling Sphere
Designing mazes for a physics sphere requires different considerations than designing them for a direct-control character. Corridor widths must accommodate the sphere’s rolling diameter with enough clearance to navigate turns without getting stuck. Dead ends need to be clearly readable — the player must be able to determine they’ve hit a dead end and turn around without the sphere losing so much momentum that it can’t exit.
Sharp 90-degree turns are particularly demanding in a physics sphere game: the sphere’s momentum carries it into the outer wall of the turn, and the player must anticipate and brake before the corner. This momentum management is what makes maze navigation in a physics game more skill-intensive than in a direct-control game — the maze itself is the same, but the physics of navigating it adds a layer of challenge that the geometry alone doesn’t convey.
Multiple levels allow the maze complexity to escalate: early levels have wide corridors and simple layouts; later levels introduce narrower passages, longer dead-end branches, and more complex route decisions that must be made while managing the sphere’s momentum.
Projectile Dodging
The projectile hazards introduce a reactive challenge that the maze alone doesn’t provide — the player must not only navigate the space but respond to incoming threats while maintaining control of a physics body. Dodging a projectile in a physics sphere game is harder than in a direct-control game because the evasive movement has momentum consequences: a sharp dodge to avoid a projectile may leave the sphere heading toward a wall or a dead end.
Projectiles are spawned from fixed emitter points in the level — turrets or hazard sources built into the cave walls — firing at a configurable interval and speed. The timing and placement of these emitters is the core design challenge: a projectile that fires too infrequently is ignorable; one that fires too frequently becomes impossible to navigate past. The sweet spot requires playtesting with the actual physics of the sphere, since theoretical timing calculations don’t account for the sphere’s momentum variance.
Crystal Collection and Particle Systems
Crystals are collectible actors placed throughout the maze — the player sphere overlaps them to collect them, triggering a pickup particle effect and incrementing the collection counter. The particle systems serve double duty: as feedback for collection events (a burst of light particles when a crystal is picked up) and as ambient atmosphere (persistent particle effects emanating from crystal formations throughout the level, making the cave feel alive and luminous).
The crystal aesthetic — glowing, light-scattering formations — is particularly well-suited to particle systems. Point lights placed at crystal locations cast colorful light pools across the cave floor. Particle emitters at crystal clusters produce slow-drifting motes of light that fill the cave with a magical, underground atmosphere. Together, the lighting and particles transform what would otherwise be a grey geometric maze into a visually distinctive environment that motivates exploration.
Multi-Level Progression
Each level is a distinct maze with its own crystal count, projectile layout, and geometry complexity. The win condition — collecting all crystals and reaching the exit — is consistent across levels, but the path to achieving it escalates in difficulty. The level transition uses OpenLevel to load the next cave section, with a brief fade transition between levels.
The multi-level structure also allows the projectile hazards to be introduced gradually: the first level might have no projectiles, establishing the maze navigation as the primary challenge; later levels add projectiles in increasing numbers and at more demanding positions relative to the maze’s narrow passages.
Reflection
The Crystal Cavern is the Marble Run’s more mechanically complete sibling — it takes the same physics sphere foundation and adds three distinct gameplay layers on top of it. The combination of maze navigation, projectile dodging, and crystal collection produces a game loop that’s more varied than any single mechanic alone, and the escalation across multiple levels gives the player a sense of progression that a single-level prototype can’t achieve.
Building this project without a tutorial — designing the maze layouts, tuning the projectile timing, deciding how crystals are distributed — required all the same judgment calls that the Endless Runner did, applied to a completely different genre. The result is one of the most complete independent games in this early series, and the one that most directly demonstrates what physics-based puzzle game design requires: understanding not just how the physics work technically, but how they feel to play through.
Nicolás Bertoa 
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