Light is the mechanic, not the lighting

A black vector screen and three gels in the printer's colours. Yellow blocks blue, magenta blocks

green, cyan blocks red — real subtractive optics, so they stack. Yellow and cyan together leave

green and nothing else. Three gels, seven usable states, and every one of them is a different

room.

What you cannot see cannot see you

Invisible is not hidden. It is absent. A wall you cannot see is not solid and you walk straight

through it. A trap you cannot see cannot cut you. An enemy you cannot see is frozen — and cannot

be shot. Visibility and collision are the same channel, so they can never disagree with each

other, and every gel swap rewrites the floor plan under your feet.

Stacking costs light

Each gel darkens the tube and tightens what you can see. Seeing one thing clearly means seeing

less of everything. And you cannot flip a wall into your own body — the swap is refused rather

than shoved through, which makes timing a gel a positional decision, not a panic button.

All three gels is total darkness

Nothing passes, so nothing exists: nothing can touch you, nothing is solid, and you can shoot

nothing at all. The tube will not hold it — after four and a half seconds a gel pops off, and

never one that would drop a wall inside you. Coming back into the light, both sides are blind:

you get a second of grace, they stand still for slightly longer. Earn it with a real stretch of

blindness; flickering the gels will not farm it.

Running is not a plan

Enemies are faster than you. The only defence is to stop something existing — which is also the

only way to stop being able to kill it. A room does not wake at full speed either: enemies hold

for a moment and wind up, dim while dormant, so you get a room to read instead of a memory test.

A hundred levels, ten tiers, one seed

Nine rooms and a boss, ten times over. The first three are hand-built because they teach the

three rules and nothing generated teaches as cleanly. Everything after is generated from the

level number, so level 34 is always the same level 34 — a run can be replayed, compared and

argued about. Each tier decides what a level is allowed to use, so the campaign teaches in order:

primaries, then secondaries only a two-gel stack erases, then walls no light gets past, then

density on top of all of it.