Forging in Rohan is the process of combining two pieces of armor or two weapons to make a stronger weapon from it.
When you forge weapons, you take normal weapons and you turn them in to ‘Rare’ weapons, which then can be combined to make ‘Unique’ weapons which can be upgraded in to ‘Ancient’ weapons. With armor, you take normal armor and make ‘Rare’ armor from it and then you can ‘Enhance’ it to make it even stronger.
Keep in mind that there are only set combinations that can be made with forging. You can’t combine any two weapons to make a new weapon. Only two specific weapons make the new weapon.
Two normal weapons make a ‘Rare’, two rares make a ‘Unique’ and adding an accessory to a ‘Unique’ will allow the making of an Ancient. The same goes for armor, except putting two normal will make a ‘Rare’ armor, putting two 'Rare' together will make a 'Unique' and the ‘Enhanced’ version is the one after it.
Advantages
Just buying two weapons from the store and combining them will give you a powerful weapon? Actually, that is probably the smallest advantage from creating a forged weapon.
The biggest advantage is the fact that when combining two weapons, the modifiers to that weapon are pulled into the next generation of that weapon.
If you have a sword that has +5 to strength and combine it with the corresponding sword that is +5 to strength, you will get a sword that gives you a whopping +10 strength bonus. This is the biggest advantage of forging weapons. Of course this takes a bit longer to get these weapons because weapons with modifiers can only be gained through quests and from enemies rarely. But the results are so much greater.
Technically, if you have two ‘Rare’ weapons that are made of four normal weapons with modifiers, that will give each ‘Rare’ both modifiers and making an ‘Unique’ from that will give it all four modifiers. Moving that to ‘Ancient’ will give it yet another modifier from the accessory it combined with.
It is quite possible to have a weapon that is stronger than a weapon that is 10+ levels(Rohan powerleveling) above it by careful combinations.
Disadvantages
The chance of breaking both pieces of equipment. That is the biggest disadvantage is the fact that your preciously created puzzle pieces can easily be shattered if you are unlucky. With each successive level the chances of success decreases. The chances of getting a ‘Rare’ item are about 50/50 or around that area.
Those chances only decrease as you move up to ‘Unique’ (It is quite possible to try and make a Unique item 10 times and fail) and even harder to make an ‘Ancient’. In fact it’s a cold day in hell when you succeed in making an Ancient.
Get by these disadvantages
Preservation stones. When a preservation stone is applied, even if you fail you will keep both of the pieces of armor or weaponry instead of them shattering in to nothingness, leaving you a sobbing mess on the floor as your preciously crafted swords crumble in to dust.
How do you get this item? From what we can tell so far, Cash Shop. It’s as easy as that. Who said they weren’t going to make Rohan gold off of it?
Source.