Theory on gate construction. Please comment on this.
1: Each "ring" has 20 slots. If a ring is filled, then either 3 or 4 levels, as appropriate, are added to the dungeon.
Filling two rings brings the dungeon down to Moorcroft.
Filling four rings brings the dungeon down to Emberlight.
Filling six rings brings the dungeon to the "fake core", what we think is the core, but we'll find out later is not.
2. Each map is a (Icon, Color, Group, map-group, map) tuple. For example, "Clockwork Tunnels" is an icon and group that has different maps for each color. "Scarlet Fortress" is a group that only has maps in red, but has at least three different maps in that color.
Full example: The icon that looks like weeds in a pond. In green (color) it is Group "Jigsaw valley", map-groups "Perimeter Promenade", "Emerald Axis", and "Jade Tangle", with two maps in each of those map groups; it is also Group "Aurora Isles" with map groups "Stone Grove", "The Jelly Farm", "Sea Petal Pass", and "The Low Gardens". The same icon in color blue is "Starlight Cradle" (group), with a map group "Shrine of Slumber" (two maps).
That gives: Icon >M Color >M Group >M Map-group >M Map.
(>M = one to many; >1 = one to one)
3. The minerals that wind up at a given depth in a ring (see dark matter tray drops, and order of tray adds) determine which color(s) are used for the maps at that depth; as much as possible, the Icon is kept constant at that depth, while the color varies based on minerals deposited. No clue how the group, map-group, and level is chosen (random?). A given icon and color will have the same group, but not always the same map group. For example, Weeds, Green, Aurora Isles, may have a depth with both Jelly Farm 2 AND Low Gardens (instead of Jelly farm 1).
4: Oddball theory: "Clockwork Tunnels", "Battle Arena", or treasure maps are always the filler if an appropriate icon is not available for a secondary color at a depth. In particular, one level was seen with Wolvers Den, Clockwork Tunnels, and Battle Arena. On the other hand, that same dungeon had a level with JUST battle arena, and one with battle arena and clockworks. (Both of these seem to discredit the idea that they are just filler. Supporting counter example: I've seen levels with nothing but clockwork tunnels, which would be pure filler in this theory.)
5. The color determines what the dominant creature type for that level is.
Yellow = Lichens
Blue = Constructs
Green = Jellies
Red = Creatures
Purple = Ghosts
This does not mean "only monster type". It means main monster type. Creatures (wolves) and Tree constructs are found on jelly levels.
6. A block is filled when enough minerals of a color are put in, OR when enough trays are put in. Putting in lots of trays with very few minerals results in those 20 spots per level having relatively few minerals per tray, and so very few levels at a given depth. Putting in lots and lots of minerals so that the 20 spots are all full results in more levels at a given depth.
In other words:
100 minerals of a color will fill a block (claimed by someone; seems reasonable). Lots of full blocks means many maps at a given depth.
Fewer minerals of a color, placed over time in lots of trays, will (I claim, untested) produce a block with fewer minerals. Lots of partly empty blocks means few maps at a given depth.
7. Dark matter weighting of trays puts the minerals deeper down. This can be used to fill up the earlier blocks by putting more trays down there. This allows you to put more minerals down deeper, which lets you put more maps down at a deeper level (and of a color that you like.)
Additional supporting observations: At the time I'm writing this, Eagle gate (far right, 4 countdown) has 7 blocks. Purple, Yellow, Blue, 2 reds, 2 greens. The bars going up have a very tall green and red, and a lot of the others. The presumption: This has close to 100 of each color in each block, so the levels where these trays wind up will have many maps (lots of minerals -- bar hight -- concentrated in very few trays -- few blocks).
Very interesting theories.
To stem confusion, let us from now on refer to each layer of depth as a "floor", and each option within a floor as a "level". This is the language used on the wiki, I believe.
A few additions:
Red creates arenas, purple creates graveyards (and possibly haunted clockworks?), and yellow creates premade levels (jigsaw valley et al).
Note that every time you see a set of premade levels, there will be a corresponding yellow bar on the display behind the gate. My hypothesis is that in order to create a set of premade levels in a certain colour, there must be (in the section of the mineral stack the gate is using to create this floor) X yellow minerals and Y minerals of the desired colour, where X > Y and Y > any other mineral in that section.
So, yellow + blue = shrine of slumber, yellow + red = cravat hall, etc.
I also hypothesise that creating a boss level (e.g. vanaduke, or stygian steeds) is as simple as just having enough yellow + other to create N floors, where N is an amount required to produce a boss level. Note that both the boss levels we've seen were preceded by a number of floors of premade levels of the same colour.