Deep Drip Depths

Deep Drip Depths is an anomalous course reportedly found in some copies of Super Mario 64. It is set around an underwater mountainside. The level is of note for its extreme, frustrating difficulty, due to its design gimmick: forcing the player to plot their route through the level to make use of the limited supply of coins. Reportedly, it is typically accessed through a trapdoor of some kind, ordinarily located on the fourth floor of the castle.

Contents
The level is expansive both horizontally and, most of all, vertically. There are no hard boundaries, but the absence of coins renders it impossible to explore beyond the intended area without drowning. Unlike other water levels, there is no reachable surface. Moving downward, the water color is reported to darken, starting with one slightly darker than Jolly Roger Bay, and ending with pitch black. Aside from the open area, a cave system is also typically reported.

Coins are relatively common, but there is no renewable source. To compensate, the coins glow with small circles of light under them instead of a shadows.

At the height at which the player spawns, the mountain appears as a flat stone wall. There are multiple holes in the wall, from wherein Unagi swim in and out. Below this point, the cliffside slopes out into a mountainside. One relatively consistent feature is the appearence of NPCs known as Slaarghs, which may either be enemies, spewing toxic brine, or, as seen in one report, friendly NPCs. Typical landmarks here include a section with hydrothermal vents and a section with more cages hanging in chains, where one needs to use the Metal Cap to jump across. At the bottom of the level, the mountainside drops off into a sharp cliff, and swimming below this point is impossible as shortly below this depth is a rapid current.

Reports
Report 1:

''Ah yes. The impossible water level. You'd spawn in a cage. and there'd be nothing you could do but exit the level or drown. What's strange was how the eels acted at first: The first time I entered, I remember one of them biting at the cage, to no avail, and afterwards, they'd just circle around me like they were waiting for me to do something. After that, it was just the circle over and over again every time I entered. A shame, because I had a feeling that whatever was beyond that corridor was something to look forward to.''

Report 2:

''Funny you'd say that. I also had that problem, and found the solution. Turns out you could bring caps into levels, including the Vanish Cap. Although, if not for the Internal Garden on the other side of the corridor, I'd call you lucky. The level was bullshit. It would be frustrating as a platformer, but it was a puzzle level, and the gimmick was hell. Who in the right mind thought it was fun to drown for the 7th time because you collected two too many coins on the way to the Rainbow Cap ten minutes ago?''

Also, did your version also have snow underwater?

''As for the gameplay, in one part, there were more cages. Some of them swinged back and forth, and when they neared their peak, you'd have to make a jump-dive maneuver to avoid sliding off. By stomping with the Metal Cap, you could crash the cages into the ground, and jump mid-fall. The star was in a cage, and you'd have to crush it on a spike. The cages fell extremely quickly, so you'd barely have time to react. Near the bottom of the level was a field of what looked like small volcanoes, which emitted toxic smoke. The smoke formed a "canopy", so you'd be forced to swim very precisely. At the same time, you were chased by homing bullets. As I said, the level was bullshit.'' ''At the bottom of the level was a steep cliff. Below the cliff, the water became a jet stream, which you could see by the snow particles racing away. A bit down the cliff were two metallic platforms, like oil platforms, with Bowser's logo. Both of them had launchers for the same homing bullets, and the lower one was just above the jet stream, so a single hit was enough to send you flying.''

I remember the final mission, "SECRET IN THE ABYSS".

''In the middle of the level was a lake of brine, which extended into a large cave. Inside was a village of strange worm creatures called Slaarghs, which I've drawn. They were appearently very stupid, because when you entered, they ambushed you and it wasn't before eating away half of your health bar they realized you weren't a fish. As the bearded one told me, there had been a strange, and according to him, disgusting, smell coming from the deep sea, growing stronger and stronger for each day.''

''I figured you could use the Metal Cap to withstand the jet stream. It ran out, but not before I saw a cave inside the wall, and managed to jump inside. What I found was very... odd. Inside was a bathhouse, with white tiled walls and a door, but you couldn't actually interact with it. There was a Toad, who seemed unbothered. He said that "FIRST THE CASTLE GREW A NEW APPENDAGE AND NOW MARIO HIMSELF SWIMS OUT OF MY POOL.", and gave me a star.''

The star registered as a castle's secret star, and the mission wasn't completed.

''That didn't satisfy me, so I kept going. The solution was to ground pound the starting cage. The puzzle to actually get there, I don't remember, except that it was very contrived and made me swear several times. What I had to do was to use all caps at once: the Wing Cap to fly, the Rainbow Cap to fly fast enough, the Vanish Cap to get into the cage, and the Metal Cap to send it crashing down. The cage fell for what felt like minutes.''

''The seafloor was covered in the "snow", which was greenish in color and probably not actual snow. I refused to touch it. There were also these big yellowish monoliths with holes, out of which came gray smoke. Some had silver stars on top of them. Every time I approached one closely, floods of gray gunk started surging out of it. Eventually, even the ones I didn't touch started erupting.''

''I was curious to see what the NPCs had said. Unsurprisingly, the smell had became far stronger, strong enough that most of the villagers found it "hard to think". Some of them loved it, saying it was the best thing they've ever experienced, while others hated it. One of them, the quest-giver, "REALLY DIDN'T LIKE IT". Ever since the smell came, he'd always had a headache. Now that I had unleashed the goop, it had slowly but steadily grown into a migraine, and he found that the water "tasted foul to breathe", like meat. Another had started feeling a "fear-headache" ever since he saw what happened to him.''

Uneased, I kept returning to the level over my playthrough, but nothing seemed to change.

Theorizing
The level's name and theme (dark water-themed level) is reminiscent of Deep Dark Galaxy from Super Mario Galaxy. It is possible that said level takes inspiration from Deep Drip Depths.

It also resembles The Ocean Depths, sharing the rock wall, dark water color, and Unagi. This could mean that the level is a cut-down version of Deep Drip Depths, that was salvaged when the level was removed, or conversely: that the Ocean Depths is a beta version, with Deep Drip Depths the final verison.