The Abandoned Waterworks is a ROM hack created by hamius8000 for the S NDBB Atmosphere Competition.
Gameplay Changes[]
Mario's ability to breathe underwater has been distinguished from his HP. Instead of his HP being depleted while underwater, he now has a thin vertical white bar next to him signifying how much breath he has left. Resurfacing does refill his breath meter by quickly replenishing it, whereas collecting coins instantly replenishes it. Resurfacing no longer recovers Mario's HP.
Fall damage has been disabled for this hack, and there is no option to save after collecting this hack's only Star- instead, the player gets sent straight to the endscreen.
Overview[]
This hack contains one level overwriting course 1, called The Tunnels; the Act shown on the pause menu is called The Flooded Passages. This level consists of a series of large grey pipes connecting several rooms, with many of the tunnels being partially or fully submerged in water.

One of the power cells
As a sign behind Mario's starting point explains, the main area in The Tunnels is low on power, and as such, Mario will need to collect at least three of the six power cells scattered around to open the door on the other side of the complex.
Once Mario has collected three or more power cells, he will need to find the control panel, approach it and press L to initiate the door-opening sequence. To find this, he'll need to enter the upper tunnel in the Chuckya/Goomba room, then swim through the submerged section through the left tunnel.
The entire complex is filled with easter eggs, largely in the form of grafitti on the walls of the rooms between the tunnels. Most of the grafitti is for BUP or resembles a cartoonish crack in the wall, but there are some notably unique ones too. One of them reads "First try IDIOT", and another in a much more hidden room reads BILL BOARD.