Hydrocity Zone intro area: the water jet

Finally, we arrive at the fourth and final element of the Hydrocity Zone intro sequence: the large jet of water that propels you out of the flooded tunnel.

The water jet is an object, and it's actually placed directly within the level's object layout. There are two subtypes of the jet object, one vertical and the other horizontal, and both can be manually placed using debug mode.

Now, it doesn't look like much until you place it because it loads its own art when it spawns, overwriting the graphics for the Turbo Spiker enemy. And although the object deletes itself and reloads the enemy art the instant it goes off-screen, there's still a known edge case in which Super Sonic can accelerate fast enough to bring a couple of Turbo Spikers into view before their art has finished decompressing.

As you play around with debug mode, you may notice that sometimes, you can't seem to place any horizontal jets. This is because the init code for the horizontal jet contains a clause which deletes the object if player 1's Y coordinate is less than $500; apparently a hack to prevent the jet from spawning when you take the top path out of the intro area.

However, this creates an oversight. If like before we take the long way around to the back of the tunnel, but avoid going near the object until we're below the $500 mark, then the water jet will shoot out for no reason as we climb up the wall.

Note how when we do this, the rotating palette remains in its slow setting. This is because the horizontal jet counts on it having been sped up by the tunnel background object, so its only responsibility it to slow the palette back down.

Which leads us to our final oversight. Possibly to avoid shooting out for no reason, when the horizontal jet deletes itself, it doesn't set its flag in the object respawn table. As a result, the jet will shoot out once and then never reappear, even if we take the long way around back to the intro area and use the tunnel exit again.

Now, this is hardly an oversight in and of itself, since it's pretty obvious that you were never meant to return to the intro area. The oversight is that since the water jet doesn't respawn, there's nobody around to slow the rotating palette back down, which means all the waterfalls are once again animating at a ridiculous speed.

The only way out of this mess is to trigger one of the vertical water jets, which respawn every single time.