Sonar

You are going down into a wreck. Your air is your budget.

The sonar does not sweep on its own: every ping costs oxygen, and permanently paints whatever it touches. The map on the screen is yours. You paid for it.

At the surface, an operator talks to you on the radio. He sees nothing. He has your telemetry and a survey of the hull made before it collapsed. He guides you with total confidence, and he is right.

At first.

The deeper you go, the further his survey drifts. Nobody tells him. He keeps asserting, with the same certainty, from data that no longer matches anything. An amber diamond starts pulsing in the middle of a wall you painted yourself thirty seconds ago.

From there, the only real question in the game: do you obey, or do you turn back to that branch you traced and left behind? Both cost air.

Below fifty metres, a ping sometimes wakes something else. Not an enemy: a surface returning from a place your own map says is empty, that never writes itself onto it, and that fades leaving nothing behind. You will not know.

There are three ways to end a dive. Drown. Surface with the black box. Or surface without it, alive, because at some point you decided to stop following him.

The end screen finally lays the two maps over each other: the compartments you actually went into, and the ones he insisted on.