The game uses many different noise generators to shape the world's terrain. It's possible to overflow these noise generators like any other in order to see their relative Far Lands, and since this mod is centered around the Far Lands it only seems fitting to be able to break these (especially seeing as most of them only break beyond the 32 bit limit with default settings, barring them from being seen otherwise). A lot of this is extrapolating from the Cubic Chunks mod, however, and as such some of the later information may not apply to vanilla (or will behave differently from expected).

The noise generators are as follows:

• Low noise and high noise: Along with selector noise, these make up what customised worlds refer to as coordinate scale (or, in the case of the y axis, height scale). Being able to configure these two noise generators separately of each other and mismatching them results in the far lands becoming extremely weird, as in this video. The low noise and high noise are responsible for the existence of the Far Lands and Fartherer Lands.

• Selector noise: This noise is responsible for the existence of Farther and Farthest Lands. Currently with the mod it cannot be configured (see #19), despite being part of coordinate scale in vanilla.

• Depth noise: Another noise generator which could be configured back in customised worlds. Not much is known about the far lands for this noise generator. Only can be scaled for the x and z axes.

• Surface block noise: The depth of dirt/grass blocks and such at a given position is controlled by a noise generator. I've managed to get this to overflow using the cubic chunks mod and customcubic: https://media.discordapp.net/attachments/347988915283558400/656907100953247765/image0.png

• Mesa noise pillar: Used for generating badlands biomes, haven't tried overflowing this.

• Mesa clay band offset noise: Used for generating badlands biomes, haven't tried overflowing this

• Swamplands noise: Used for generating those weird random patches of mixed water and grass you get in swamps. Haven't tried overflowing this

• Flower distribution noise: Haven't tried overflowing this

• Many other noise generators used for generating biome-specific features, most of which probably don't affect much significant stuff and which overflow far beyond accessible distances. Overflowing these might result in some relatively minor craziness.

It's worth noting that there are many different factors which affect what points noise generators overflow at. For example, even though selector noise has a considerably higher period than the low and high noise, only half as many octaves of it are used, resulting in it being generated 256 or so times farther out than one may expect, so these will need to be taken into consideration for calculating predicted overflow points.

closing as the notice on this mod's readme has announced discontinuation for a while now - feel free to reopen in future if work starts again

I think some of these (like the surface block filler) actually use simplex noise in vanilla, instead of perlin noise, so the effects will probably end up being different. Not sure how difficult it would be to have an option to switch between perlin and simplex noise for each noise generator to see the different ways they can break.