There are several add-ons for version 0.13 of Mystcraft. These can be created by anyone with a knowledge of Java and may change or add to mechanics introduced by Mystcraft.
Linking Through the Ages
Linking Through the Ages is an in-game guidebook for Mystcraft, since Mystcraft does not currently have one. There is an additional volume (obtainable as loot) that explains the Narayani symbols found on Mystcraft's various page.
CurseForge Project: https://minecraft.curseforge.com/projects/ltta
Source Code: https://github.com/TheFloydman/LTTA
linking-tweaks allows users to change how Mystcraft's linking mechanics work.
CurseForge Project: https://minecraft.curseforge.com/projects/linking-tweaks
Source Code: https://gitlab.com/veovis.muaddib/linking-tweaks/
More Mystcraft is a collection of miscellaneous additions to Mystcraft, including structures, Age features, and pages for various biome distributions.
CurseForge Project: https://minecraft.curseforge.com/projects/more-mystcraft
Source Code: https://github.com/TheFloydman/More-Mystcraft
Mystcraft BoP Disabler
Mystcraft BoP Disabler disables the pages Mystcraft generated for Biomes o' Plenty biomes. Those biomes currently come out flat in Mystcraft Ages, but are otherwise functional, so this mod is cosmetic only. (This is only true for Minecraft version 1.12.2, BoP biomes generate properly in Minecraft 1.7.10 and earlier.)
CurseForge Project: https://minecraft.curseforge.com/projects/mystcraft-bop-disabler
myscraft-info adds tooltips when hovering over Mystcraft pages with the cursor. The tooltips are configurable and allow the player to see the translations for the symbols on the page as well as how the page can be used in a Descriptive Book.
CurseForge Project: https://minecraft.curseforge.com/projects/mystcraft-info
Source Code: https://gitlab.com/veovis.muaddib/mystcraft-info
Pages adds block pages for many vanilla and mod blocks that Myscraft does not add natively. It also allows users to tweak the rules governing those blocks as well as to add their own blocks.
CurseForge Project: https://minecraft.curseforge.com/projects/pages
Source Code: https://github.com/TheFloydman/Pages
Mystcraft/Mystic World - Ghen's Ink Recipe
Alters Mystcraft's ink vial recipe to use beetles from Mystic World.