Sonic CD's take on the classic Labyrinth Zone, an aquatic cavern level complete with heavy use of typical underwater segments, and winding, narrow passageways loaded with steps and vertical drops. There are plenty of puzzling objects to contend with, including water currents that carry Sonic in one direction, manipulated by switches that also open many a doorway, and lots of tricky moving blocks and spikeballs. Straight paths above the water take you across the most part of the zones, with several gaps to drop down to submerged routes below, and while this is not a fast level, there are a few areas that provide easy time travel between two springs.
This water cavern level is clearly modelled on Sonic 1's Labyrinth Zone, but that's ok, because it brings plenty of original visual content too. In the Present, you'll start off in a small external area outside, before plunging into the rocky passageways that occupy the rest of the stage. This brief view of the outside, exclusive to the Present, is a rather dark affair, featuring rocky volcanoes that periodically burst with fire and magma with uncanny synchronisation, a spectacle that briefly lights up the otherwise dark night sky. The rectangular peaks of red and blue rocks spread for miles, below it.
Meanwhile, the background for the internal caves that occupy the majority of the stage relies, much like Labyrinth, on a basic wall of large stone blocks, some depicting patterns, others are covered in a network of large cracks. They are all either intruding or extruding from the wall, which is a very dull brown-ish red sort of colour that becomes green and constantly ripples when you view it from underwater. As for the foreground on which the paths are cut into, it's mostly a mix of odd orange and yellow polka dot blocks that extrude in thin, Tetris-like strips, and light blue cracked bricks and patterned blocks that largely cover the paths that Sonic can walk on. There are occasional light blue pipes stretching across the foreground and out of ceilings, and various stone pillars and structures standing along the paths, mostly decayed and some slanted, alongside strange purple cave-dwelling plant-life on both the floors and ceilings.
Things are a bit less man-made in the Past, as you would assume, and what will one day be a wall of huge patterned bricks is now just more of a collection of spiky cave rocks in the background. They're light brown and green, with large gaping black holes appearing quite regularly. The foreground has changed from orange and yellow polka dot to lime green and yellow polka dot, while the bricks along the surfaces of the paths are grey and quite old-looking, and similar tall pillars stand along the paths. Replacing the weird plant life from the Present are small, withered brown plants with thin vines. You can also find occasional patches of stubby grass and smaller plant-life along floors and ceilings, and despite this being the Past, there are still a few questionable pipes sitting around, for some reason. The water here seems to give everything a darker tint than normal.
The Good Future is very much more mechanised, but a good kind of mechanised, obviously. It's kind of a healthy containment area for plants and the water, and the background wall, dark green and purple, is now filled with containment tubes for the plants, and pipes and other little technical paraphernalia run throughout it. The polka dot foreground is now pink/megenta-ish (blue when viewed underwater), with shiny light blue panels to walk around on across the surfaces, and formerly rocky patterned blocks are now made up of hi-tech gubbins. Technical piping and meters act as typical pathway decoration, and plants, both inside and outside small glass containers pop up all over the place, even in small platform blocks that you can stand on.
The Bad Future meanwhile is essentially a darker and much more decrepit version of the good alternative. The mechanical background wall has no trace of healthy plant containers and is more of a mass of orange, black and green piping and panels, some old and broken, with a few small, static lights. The polka dot patterned foreground has settled on a plain grey colour now, and bricks along the floors are a rusty brown, with mechanised gubbins and lights, and there's usually a thin metal panel along the absolute surface of the floors. Blocks sporting Eggman's face also appear quite regularly. Pillars are now mechanical and in a condition that's far from new, pipes have become extremely rusty, and the last few plants hang dead from the ceilings and floors, their parts barely clinging together. The water is also much darker and murkier, and gives the level a dark purple tint when under.
Tidal Tempest employs a real maze structure if ever I did see one. The paths operate much like Labyrinth Zone, so don't expect speedy, looping roads or curved walls, and do expect flat pathways, plenty of steps and separated block platforms to climb up and down vertical passages, and occasional slopes that are always at the same angle, and awkward to climb back up. All this takes place inside small, slow-moving corridors and chambers, most of which are covered by water, making them even slower. While Labyrinth Zone had an individual, enclosed path meandering its way through a large chunk of ground with little deviations, Tidal Tempest is much better at using its space efficiently, and crams multiple pathways across the whole map, most of which primarily lead right, with an upper path and a lower path running at the same time in most places. Common for both Zone 1 and 2, the upper path is usually very straight and simple, and spends much of its time above the water level, though it has plenty of gaps in the path to drop down below. The Lower path engages you with a variety of obstacles underwater, where you'll constantly have to keep an eye out for more oxygen to keep you going (more on that in a mo, if you're a bit rusty with your water stages). Meanwhile, a series of vertical passages link the two together in the middle, so you can switch between each route at certain places, using a range of objects and structural designs. So obviously, the ideal solution is to stick to the top routes, and you don't even have to delve too far into those lower regions to find the hidden machines in the Past, or even opportunities for time travel either.
The water level rises and falls at various points, but largely occupies most of the map, so inevitably, you will have to dip your toe in now and then, where you'll notice that Sonic's actions become much slower as he wanders around down there. When you drop in, you only get 30 seconds worth of air before you run out, and during the last 10 seconds, an on-screen countdown going from 5 to 0 will alert you that you're running out of air and need to get your ass in gear. If you reach the end of the countdown, Sonic will drown and you'll lose a life. To prevent this, either get out of the water or locate a small cluster of bubbles on the floor. Make contact with the big bubbles that they produce to suck up another 30 seconds worth of air. Sonic is quite prone to being caught up in water currents which will propel him uncontrollably in various directions, either around a large chamber so that you can access a high ledge, or through a long winding passageway, etc. Long, large glass tubes can also offer a transportation method from A to B, and there are occasional hidden rooms and routes inside the ground containing hidden items and soforth. The Past versions of both zones tend to be able to offer better ability to backtrack across the stage, while other time zones may not allow you to re-visit previous areas due to high ledges or passageways that close behind you as you leave them. This is particularly true of the Present, and means you'll only get a limited chance to take advantage of the available time travel posts.
Tidal Tempest has a huge range of different objects to encounter, some of them just one-offs and several can only be found in a particular time zone. They're quite difficult to organise into a few paragraphs, so forgive me if I miss anything or skip some details. First and foremost, grey switches that are triggered by standing on them are an extremely common, puzzle-oriented object that have a variety of uses. They typically open nearby doorways, either small horizontal or vertical hatches in passageways, or thick blockades that are made up of a number of long vertical doors (those usually lead to hidden power-ups, often in hidden rooms in the wall). Sometimes you may need to stay standing on the switch in order to get past the obstacle, such as in Zone 1 Present where a switch is positioned on a chained platform that swings around 360 degrees, going through a door that only opens when you're standing on the switch. Further underwater, a switch is placed on a pair of long thin platforms that only rise up to the upper ledge when you're standing on it.
The current of the water in some submerged sections is also controlled by switches. Nearby, small propellers in the floor or walls will activate, creating an invisible force in the water that can carry Sonic along a particular direction when he jumps into it. This is commonly a one-way route through a series of corridors, or it may take you in a circular or zigzag fashion through a large room. You usually have little control while this is happening, but sometimes you can break free of the current using the left and right buttons, perhaps to get off at a ledge. When being thrown through a corridor, it's usually possible to alter your vertical co-ordinates using the up and down buttons, but you can't stop until the current's had enough with you. Sometimes you may find two switches either end of the path of the current, each one changing its direction so that the current will take you to the other end. While we're on the subject of water, I hope I can assume that you know by now that Sonic can only last 30 seconds without air down there. To refresh your supply, look for the small clusters of bubbles that sit on the ground in submerged sections. After a few seconds of waiting (if you have them to spare that is), it'll start producing large bubbles that you can suck up for another 30 second refill.
Moving blocks and platforms come in all shapes and sizes across the time zones. Some large and square, others thin and horizontal, but there tends to be several of them in one place, moving in a particular pattern, so you may need to try and study it first to see where you can best make your move. They're often solid so they will be able to crush you into a wall or another block. Watch out for statue faces on the walls, near the floor. Similar idea to those in Labyrinth Zone, but these shoot a constant stream of water blasts which aren't directly harmful, but will force you in their direction along the ground if you make contact, and this can often mean falling down pits and vertical passages. Watch out for the odd small spikeball on a long chain, swinging all the way round, and other spikeballs will just sit there in the air completely motionless, like mines waiting for you to come along and get hit. These may often appear when a water current is forcing you along a submerged corridor, though fortunately there may be a pole right in front of them that Sonic will automatically grab onto. As is commonplace in these water levels, you can move Sonic up and down the pole with the up and down buttons to get out of alignment with the spikeballs, and then press a jump button to release him and evade them. Leave him hanging on there too long and he'll let go by himself after a few seconds.
Weak ground is identified by a thin, cracked section of rock that will collapse when you stand on it, but this is often necessary to progress either downwards or upwards through vertical passageways and shafts. Be aware of long, thin hanging pillars with sets of spikes pointing downwards just above the floor. These will fall in a rather stop-starty fashion as you pass by and are easily avoided, but they can instantly crush you should you be foolish enough to get caught underneath. Same for large vertical crushers that appear in the Past and Futures, which move up and down fluidly and can catch you off-guard due to the height of the gap that they can create before coming down. Underwater, you can progress up steep slopes using a small platform block that acts as an elevator. Starting at the bottom of the slope, it'll begin rising as soon as you step on it, but won't go back for the return journey afterwards, so try and stay on it. If you fall back down the slope, you'll just have to try and jump back up it as best you can. At one point in Zone 2 Present, the water level will rise as you step on a small wooden platform that floats on the surface. You can control the direction of this platform by running left or right, which you'll have to use to navigate a zigzagging corridor. see Point #7 for details. In Zone 1, there are two long transportation tubes, one at the start of the zone leading to a brief alternate route, and the other surrounding the machine towards the end. This delivers the same affect as the regular water current features, and will carry you along it when you jump in, only delivering one way.
Many of these more diverse objects are only found in the Present, while the other time zones have a few small tricks of their very own. One feature the Past has that other time zones don't are small L-shaped platforms made up of three blocks. There will always be two blocks aligned vertically in the middle, but the third block typically alternates between the top right and top left sides of the the pair whenever you stand on it, so it's easy to fall off. You can stand on the top middle block without anything changing though. Other versions of this object basically have an L shape that can rotate all the way around when you step on the block that's sticking out of the side. The Good and Bad Futures have groups of three, chained platforms moving quickly around a circular path. These often go through walls, so you'll need to jump off to a ledge quickly or get pushed off, and groups of spikeballs are also known to float around a similar circular or oval-shaped invisible circuit. See Point #8 for a one-off platform block that constantly descends until you step on it, where it'll take you upwards, near the end of Zone 2.
Enemies include both underwater and.. overwater attackers. Large green dragonfly robots hover around in the upper regions of the level, above water, and just buzz back and forth over a set area, with the older ones buzzing a little slower, with much less bounce to their hovering. The blue crab-like enemies that jump out of waterfalls in Palmtree Panic make an encore appearance here, only with a completely different sprite that sees them swimming around underwater in profile. When they lock eyes on you, they release several really really tiny spikes from their back that fly out all around them, but I'm not convinced that these teeny spikes hurt you or have any effect on you whatsoever, so it's a rather pointless action on their part. In addition to that however, they also charge towards you rather quickly, which is much more effective, and the damaged ones have no spikes, so they don't even bother to attempt either attack. On the surface of the water are small thin green insect bots that glide across it, and occasionally shoot out small light blue projectiles straight ahead, which the damaged ones are predictably incapable of doing. Rather ugly crayfish robots hang around near the floors of submerged routes. When they see you, they'll dive in your direction in a huge leap, while the much more damaged-looking ones at least make an effort, but their lunge is significantly less impressive. The flowers these enemies produce feature yellow, wavy petals, a zig-zagging green stem and red stigma.
- In the Sonic CD on Sonic Gems Collection, someone has seen fit to tinker with all the colouration in the water in each time zone. In the Present, the water should be coloured green, dark yellow-ish in the Past, light blue in the Good Future, and dark purple in the Bad. In Gems, the water isn't coloured at all, and the graphics look exactly the same as they do when seen above water, except for the ripples in the background, which give away the difference. I've no idea why they were taken out, but there's probably a good reason. In the original Mega CD version and even the PC version, which is actually used in Sonic Gems, the water remains interestingly coloured.