1.12.2 is a utopia for pack devs, there are a ton of mods that alter various things in the game and it feels like we're getting a few new pack-dev focused mod every week. And since there's so many of them now I have probably missed a few.
https://www.youtube.com/watch?v=QLy3Z8cmUl4
- Crafttweaker - Can tweak most things there are to tweak, all hail Crafttweaker.
- Fabricate - A in the works alternative to CraftTweaker that uses javascript instead of zenscript.
- ContentTweaker - custom items/blocks/enchants/fluids/creative tabs
- ModTweaker - Adds CrT support for various machines and registries
- LootTweaker - Alter existing Loot Tables through CrT
- ArtisanWorktables - Custom crafting tables with fluid crafting, tiers and a ton of extra tools.
- Extended Crafting - Custom crafting for 3x3, 5x5, 7x7, and 9x9 crafting tables. Also have a "combination crafting" multiblock that allows for pedestal style crafting.
- TreeTweaker - Highly customizable tree spawning rules & custom trees
- Initial Inventory - Specify what items the player should start with.
- Advanced Mortars - Custom mortar recipes which could be nice early game.
- Alfinivia - Adds liquid interactions, and some stuff to Misty World and IE, a lot like Modtweaker.
- PackMode - Pack modes similar to 1.7.10 packs, script files can be attached to a certain mode with CrT preprocessors.
- ArmoreableMobs - Give mobs armor/items on spawn using CraftTweaker.
- Modular Machinery - Custom multiblock machines, recipes for the machines can be added in JSON or through Crafttweaker.
- UniDict - Unifies metals and machine outputs of said metals, very powerful. Have a few methods in Crafttweaker.
- Dropt - Powerful drop replacer for blocks with a ton of rules and modifiers. JSON Based
- Block Drops Tweaker - Similar to Dropt, also JSON based. Have commands to help with rule creation.
- Scavenge - JSON based tweaker that let you scavenge items from blocks, can have rules like that the player has to sneak to scavenge, or that the block has x amounts of uses.
- Gendustry - Can makes custom bees, combs and bee mutations for Forestry
- Block Tweaker - Tweak properties of existing blocks.
- Ex Nihilo Creatio - Config can be changed so it uses json lists for its recipes. Not exactly a pack dev mod but it's really versatile.
- Erosion 2 - Block fluid erosion, will transform certain blocks under the right conditions.
- Restriction - JSON based tweaker that let you limit the players ability to place Blocks/TileEntities depending on a set of rules. Will not stop placed TileEntities from working but it will block any tries to open the GUI if the conditions are not met.
- Dimensional Control - Tweaks dimensions. Can do powerful stuff like block replacing at certain Y levels, custom portal structures and more.
- Just Enough Dimensions - JSON based custom dimensions.
- The Lost Cities - A custom dimension for city-like landscapes, but it's profile system is very powerful when paired with Just Enough Dimensions.
- Void Island Control - Highly customizable void dimension control, can generate islands from minecraft structure data.
- Advanced Rocketry - Included in this list since it can be used to make custom planet dimensions.
- CoFH World - Ore, lakes & biome decorators like bushes grass etc. Very powerful. JSON Based.
- Ore Tweaker - Oregen configured through a config file, can disable vanilla ore gen and do it's own custom ore gen.
- Hex Lands - tile based world generation.
- Worley's Caves - Overhaul of vanilla cavegen, adds continuous larger caves.
- Cave Generator - Overhaul of vanilla cavegen, can be tweaked with custom presets.
- Biome Tweaker - Tweak existing biomes or make custom ones
- Biome Tweaker Core - Coremod addition to biometweaker, allows for some extra tweaks like foilagecolors.
- Recurrent Complex - Versatile custom structure generation system
- Pillar - Easier recurrent complex alternative, json based. Generate structures in the world with the use of structure blocks.
- Roguelike Dungeons - Dungeon mod that comes with a few new dungeons, but you can make custom dungeons where most things are tweakable.
- In Control! - Very powerful JSON based mod that can set spawning rules, and tweak mob properties on spawn.
- Better Questing - Questing mod with a very good quest designer. preferable to HQM since HQM has no release version for 1.12, only beta.
- "Better Questing - Standard Expansion" - Adds Tasks/Rewards/Themes etc. absolutely required to do anything with Better Questing.
- Triumph - Custom advancements. Best used with Better Advancements.
- Better Advancements - Improves the UX of the vanilla advancement GUI.
- Game Stages - Base API, required for all of the gamestage AddOn mods.
- Recipe Stages - Hide and disable certain recipes until the player has a certain stage.
- MultiBlock Stages - Require the player to have stage X to be able to construct a specific multiblock.
- Ore Stages - Can hide ores behind gamestages, hidden ores can be masked as a different block.
- Gamestage Books - Consumable books that unlocks GameStages, mostly added for an alternative to unlocking gamestages by commands.
- TellMe - Mod for dumping metadata for your minecraft instance. Sometimes you want to dump data which crafttweaker cannot dump, for example a list of registered enchantments. Can give information about most things that have a registry.
- Controlling - Searchable keybinds, Not a pack dev mod per say, but something every pack should have.
- FastWorkbench - Important performance mod for 1.12, caches recipes so the game does not do a full recipe lookup for every recipe when batch crafting.
- Preston - Block compression for all blocks in the game, you can configure how many compression levels a block have.
- Custom Main Menu - Tweaker for the main menu, can alter buttons, backgrounds etc.
- Resource Loader - Custom resourceloader thats helpful with Custom Main Menu
- LaunchGUI - Displays custom messages when the modpack is launched.
- Pickle Tweaks - Adds crafting grid repairing of tools, information tooltips and right clicking crops.
- World Stripper - Can strip out configured blocks from your world so it's easier to see how your oregen or cavegen looks.
- Water Control Extreme - Limits the minecraft behaviour of having infinite water
- Custom Tweaks - Various meta tweaks to packs, like changing the window title of the java process & encouraging users to update the pack to the latest version.
- Material Changer - Changes properties for certain materials.
- Infini-TiC - JSON based way to add additional materials to Tinkers Construct.
- Tweakers Construct - Minor Tinkers Construct addition that lets you tweak base durability, cost of parts, and removing tool materials.