You drop the box from the tunnel, expect the nearby Hidden Box to reveal, and nothing happens.
That is the trap.
Tunnels look simple at first. They are the blue tube-like blockers with a number on the front. In the image, each tunnel shows 3, which means there are three boxes stored inside that tunnel. The box you see at the tunnel exit is only the first one. More are waiting behind it, and the game will not show them until you clear the current one.
That number matters more than it looks. A tunnel is not just a stack of boxes. It also blocks normal reveal rules, hides key colors, and can slow down the whole board until your conveyor gets packed with marbles.
Tiny number. Huge problem.
A Tunnel is a blocker feature that stores multiple boxes inside one position. Instead of showing all boxes on the board at once, the tunnel feeds them out one by one.
Here is the basic rule:
So if a tunnel shows 3, you need to handle three boxes from that tunnel before it is fully cleared. You cannot skip to the second or third box. You cannot see the full stack early. You have to work through it.
That is why tunnels are dangerous in harder Marble Sort levels. They hide information. You may need a yellow box right now, but the yellow might be the last box inside the tunnel. Until you clear the earlier boxes, you are guessing.
Bad guesses fill the conveyor.
The number on a Tunnel tells you how many boxes are still inside. It is not a countdown timer. It does not mean how many marbles you need. It only tracks the tunnel’s stored boxes.
For example:
Each time the current tunnel box is dropped or used, the next stored box becomes available. The tunnel keeps feeding boxes until it runs out.
This creates a slow reveal pattern. You do not get the whole board at the start. You earn the board piece by piece.
That matters because Marble Sort is built around matching marbles to the correct bottom boxes before the conveyor jams. If the tunnel hides a needed color, you may be forced to delay certain marble drops until the correct box appears.
Do not rush here. Tunnel levels punish fast tapping.
This is the part that catches most players.
Normally, a Hidden Box reveals its color when one of the nearby boxes opens or drops. That rule makes sense on regular boards. Clear a box next to the grey question mark, and the hidden color appears.
But Tunnels change that rule.
If a Hidden Box is next to a tunnel box, and the tunnel still has boxes inside, dropping that tunnel box will not reveal the hidden one. The Hidden Box stays covered until the tunnel is fully cleared and the tunnel number reaches 0.
That means a tunnel can block the normal reveal path.
This feels strange because the visible box is next to the hidden one. You drop it. You expect the grey ? to flip over. It does not. The reason is that the game treats the tunnel as unfinished while boxes remain inside it.
The tunnel is still occupying the reveal logic.
So the rule is:
This is why tunnel levels often feel blocked even when you are making correct moves. You are clearing boxes, but the board refuses to give you new information until the tunnel stack is gone.
Annoying. Intentional.
Tunnels create three problems at once.
First, they hide colors. You cannot see every box you will need, so planning becomes harder. A color that looks missing may simply be buried inside the tunnel.
Second, they delay Hidden Box reveals. A nearby grey ? may stay hidden much longer than expected, especially if the tunnel starts with a high number.
Third, they can jam the conveyor. If you keep dropping marbles while waiting for the right box to come out, the conveyor fills up fast. Once the conveyor is packed and no matching slots are available, the level collapses.
That is the real danger. The tunnel itself does not make you lose. The delay does.
A hard tunnel level often works like this:
That is why some levels feel unfair on the first attempt. They are testing whether you understand the tunnel order, not just whether you can match colors.
The best tunnel strategy is simple: clear tunnel boxes early, but only when the board can safely handle the color.
Do not ignore tunnels until the end. That gives them too much control over the board. The longer a tunnel stays full, the longer it hides boxes and blocks nearby Hidden Boxes.
Use this plan:
Start with the highest tunnel number
Prioritize tunnels beside Hidden Boxes
Do not drop random marbles just to force progress
Watch the tunnel’s final box
Keep at least one safe match available
The key is controlled pressure. You want to reduce the tunnel number, but not at the cost of flooding the conveyor.
The biggest mistake is treating a Tunnel like a normal box. It is not normal. It is a box stack with extra blocking rules.
Players also waste moves expecting a nearby Hidden Box to reveal too early. If the tunnel still shows 2 or 1, that hidden box may stay covered. Plan as if you will not see it until the tunnel is empty.
Another mistake is clearing the wrong side first. If one tunnel is touching several Hidden Boxes and another tunnel is isolated, clear the connected tunnel first. It gives more value because it releases boxes and opens hidden information.
One more trap: dropping marbles because “the color will probably appear soon.” That guess gets punished. If the tunnel has multiple boxes left, the color you need might still be two layers away. Hold back unless the conveyor has space.
Use boosters only when the tunnel has already trapped you. Do not waste them at the first sign of pressure.
The best time to use a booster is when:
A Shuffle Booster can help if the bottom slots are bad and the conveyor has too many unmatched marbles. A Magnet Booster is better when one specific box needs to drop into place. A Cannon Booster is the panic button when the conveyor is already clogged.
Use the smallest fix that saves the level. Do not spend a big booster when one smart tunnel clear would do the job.
If a tunnel is sitting beside a Hidden Box, count the tunnel down before you commit too many marbles to the conveyor. The messy trick is to leave one easy color ready at the bottom, then clear the tunnel box when that color can instantly score. This lets you reduce the tunnel number without adding dead weight to the conveyor.
Even better, if there are two tunnels, clear the one touching the most grey ? boxes first. It usually opens the board faster and exposes the color the level is trying to hide.
The final tunnel box is often the dirty little trick. Expect it to be the color you needed five moves ago.
Clear the Tunnel to release hidden boxes and reveal nearby colors.
That one sentence covers the whole mechanic. The tunnel number tells you how many boxes remain, the tunnel feeds them out one by one, and nearby Hidden Boxes may not reveal until the tunnel is empty.
Play tunnel levels slowly. Clear the stack. Protect the conveyor.
Then the board starts making sense.
