Duplicate what they had in the past. They won't add it back again, so safe to add.

This is what they had in 1.12.x, needs verified what can be brought back safely. Note: I think this stuff works for 1.12, but really doesn't work with current TCon. I think some of the concepts are good, so we can move forward with the essence of this, but something that fits TCon 3.x better.

• Fiery Toolparts are toolparts made by casting toolparts with Molten Fiery. This tool material is quite versatile in use, able to be used in all toolparts, excluding Fletchings. Common traits with Fiery Toolparts are their reasonable durability, high mining level and a good attack damage. Like the Fiery Pickaxe and Fiery Sword, the Fiery Toolparts are all about using heat and fire to the user's advantage. Though Fiery Toolparts deal with fire and heat, they're still able to be held with bare hands without burning the wielder.
  • Durability: 720
  • Mining Speed: 8
  • Attack: 7.6
  • Traits: Twilit & Flammable
  • Mining Level: Obsidian
• Knightmetal Toolparts are toolparts made by casting toolparts with Molten Knightmetal. This tool material sturdy, durable and tough, which makes it perfect for melee weapons, but too tough for Bowlimbs, Arrow Shafts or Fletchers. Despite this, they have the highest mining Level, a great amount of durability or modifier, and may grant Resistance when an Entity is struck. It's a perfect material for those who want stronger weapons and prefer to stay close to their targets.
  • Durability: 1200
  • Mining Speed: 8
  • Attack: 7
  • Traits: Twilit & Stalwart
  • Mining Level: Cobalt
• Naga Scale Toolparts are toolparts made by taking Naga Scales to a Part Builder and assembling into toolparts. This tool material is not too versatile in use, with it only being used for Head toolparts and Arrow Shafts. Despite the setback of the selection of toolparts, Naga Scale Toolparts are perfect for dire situations, where if the user is in a pinch for health, the attacks become faster than normal. This speed boost can be likened to how the Naga picks up speed as it's health depletes. Players are warned, however, that they themselves will not be any faster, so it's advised to not run from battle, and charge head-first, just like the Naga would.
  • Durability: 460
  • Mining Speed: 8.9
  • Attack: 4.3
  • Traits: Twilit & Precipitate
  • Mining Level: Iron
• Steeleaf Toolparts are toolparts made by taking Steeleaf to a Part Builder and assembling into toolparts. This tool material is the most adaptable tool material added by the Twilight Forest mod, being able to be used in all toolparts. Though they are strong, speedy and have a high mining level for a bunch of leaves, their durability is weak. Despite the low durability, Steeleaf Toolparts are one with your hotbar, using the Steeleaves from your hotbar to repair itself. The tool will not consume them, but the amount of Steeleaves in your hotbar will depend on how fast it can repair.
  • Durability: 180
  • Mining Speed: 8
  • Attack: 7
  • Traits: Twilit & Synergy
  • Mining Level: Diamond
• Raven's Feather Toolparts, or more to the point, Raven's Feather Toolpart, is a toolpart made by taking Raven's Feathers to a Part Builder and assembling into a toolpart. Unlike other toolparts, the Raven's Feather is only used to make Raven's Feather Fletchings. This shouldn't dishearten the user, as its Trait allows projectiles to turn invisible. Now it is possible to sneak in attacks on your mortal enemy, and they will never suspect a thing.

Traits

• Precipitate is a Trait that can be found on Naga Scale Toolparts. This trait, depending on the amount of health left by the user, will begin to gain a speed boost. This speed boost is similar to how the Naga gains speed as its health diminishes
• Synergy is a Trait that can be found on all Steeleaf toolparts. This trait will find any Steeleaves in your hotbar, and repair the tool if there are any Steeleaves. Thankfully, Steeleaves are not consumed during the process, but it will not work if there are no Steeleaves in the hotbar and they are in the player's inventory.
• Stalwart is a Trait that can be found on all Knightmetal toolparts. This trait will, at random, grant the Resistance effect on the user for a short time when a target is struck. Despite the upside of granting a bit of Resistance, it is still advised to not run head-first into battle.
• Veiled is a Trait that can be found on a Raven's Feather Fletching. This trait will make the projectile turn invisible when fired. This can be useful for surprising your targets without showing off who or what struck them.
• Twilit is a Trait that can be found on all toolparts. This Trait either changes the speed or damage of a weapon, depending on which dimension the user is in. If the player is in the Twilight Forest while using this tool, it will gain a speed boost. Outside of the Twilight Forest, which can also include other dimensions that are not the Overworld, the weapon will gain an attack or damage boost.

Smeltery

• Molten Knightmetal is the liquid form of Knightmetal Ingots that can be used to create various Knightmetal Tool Parts.
• Molten Fiery is the liquid form of Fiery Ingots that can be used to create various Fiery Tool Parts.
• Fiery Essence is a liquid that can be used to fuel the Smeltery. There is currently no way to obtain a Fiery Essence Bucket, but it is still usable in a Seared Tank. When used for the Smeltery, Fiery Essence can reach a smelting temperature of 1000.

Current Twighlight Forest:

• Materials
  • Ironwood - A crafted material using Liveroot
    • Armor and tools are uninspiring, but could be used as a modifier ingredient. Material is Iron level, so not very interesting to make tools out of.
  • Fiery Ingot - A crafted material using Fiery Tears or Fiery Blood
    • Armor adds an ability that burns attackers (Fiery Modifier does this already, maybe an alternative Fiery Recipe using Fiery Ingots instead of blaze powder)
    • Pickaxe adds autosmelting (Autosmelt exists, maybe an alternative recipe? However, recipe is already super cheap, so not sure what the gain would be here)
    • Sword adds ability that burns targets (Fiery Modifier does this already, maybe an alternative Fiery Recipe using Fiery Ingots instead of blaze powder)
  • Steeleaf - Drop in TF
    • Armor adds a single enchantment (not very good)
    • Tools add a single enchantment (not very good)
  • Knightmetal - Obtained smelting armor shard clusters (9 armor shards)
    • Armor adds extra armor and toughness
    • Weapon/Tools do extra damage to armored targets (could be a modifier using ingots)
  • Alpha Yeti Fur
    • Has thorns effect that chills attackers (effectively similar to Freezing ... alternative recipe?)
  • Naga Scale
    • Adds fire protection III to chestplate or pants

Conclusion:
There just aren't that many interesting things for integration, which is likely why it was dropped. Most of the things in TF are well suited to Vanilla, not modded MC. Adding alternative recipes for Fiery, Freezing, Autosmelting, etc. will work. Also, some of the obtainable tools like the ore magnet could easily have ability integration into tools.

Integrations to be done after review of 2.x TCon integration and current TF:

• Precipitate: speed is increased as health is reduced - (maxHealth - entity.getHealth()) / maxHealth
  • Recipe: 5 naga scales
  • The last standing escape plan.
  • The less health you have, the speedier it is!
• Fiery
  • Alternate recipe: 1 fiery ingot per level
  • Increases max level to 7
• Freezing
  • Alternate recipe: 1 Arctic Fur per level
  • Increases max level to 5
• Autosmelt
  • Alternate recipe: 3 fiery ingots
• Twilit: 2x mining speed in Twilight Forest (similar to 1.12 modifier) 10% velocity (bows) 1.5x damage outside Twilight Forest
  • Recipe: 1 Fiery ingot 3 Steeleaf ingots 1 Naga scale
  • The Twilight Forest's illuminating blessing.
  • Speedier in the Twilight Forest. More damage outside the Twilight Forest

I was about to say that it already had integration lol.

I guess they removed it in 1.19, and if so I'm kinda wondering why.