Reforge

Reforging is a service provided by the Goblin Tinkerer to randomize the additional mods to a base item. Items will often have random modifiers when found or crafted, but reforging allows the player to "reroll" and get new modifiers without having to find or craft more items.

Accessory modifiers will grant a bonus to one of a player's stats, such as defense, movement speed, or max mana, which is applied as long as it is equipped. Weapon modifiers alter the stats of that particular weapon and may be positive or negative, with up to 5 positive or 3 negative bonuses at once. Modifiers can raise or lower the tier (rarity) of an item by up to 2 tiers, based on how good or bad the modifiers are. The displayed stats may vary depending on the item's base values, which are multiplied with a fixed value and then rounded. For example, the Murderous prefix on a Handgun will display a 7% damage increase, while a Magic Missile will display a 9% increase.

The process is expensive, and is probably intended as a "gold sink." If the item is crafted, one means of generating new mods is to rebuild the item; that may not be practical, hence the "Reforge" option on the Tinkerer. Currently, the Goblin Tinkerer charges the item's current value (5 times the sell value). A modifier will raise or lower the value of an item, so items with poor modifiers are cheaper to reforge, while reforging an already well-modified item will be more expensive.

It should be noted that an item with mods can be used in the crafting of other items if it is marked as a material. Doing so does not preserve the mods; an Enchanted Boomerang's mods are lost when used to create a Flamarang, which will get new mods randomly assigned upon creation. Thus, if you have a weapon or accessory that already has useful mods, you may wish to consider finding another of the same to use in crafting.

There are 112 different reforge modifications in total at the moment.

Accessory Mods
Accessory mods are active when equipped. Every accessory item can be reforged with the exception of Guide Voodoo Doll and all Music Boxes. Accessories can have one of the following mods attached to them:

Weapon mods
These mods only apply when the weapon is being used. Weapons that have no Knockback cannot be reforged with mods that change Knockback, such as Drills, Magical Harp and others.

The Light Disc cannot have modifiers.

Universal
Flails, Spears, Boomerangs (except for the Light Disc), Chainsaws and Drills (including the Hamdrax) can only have universal prefixes. Universal mods can also be found on all other weapon types. The best universal prefix is Godly.

Displayed values may differ due to rounding.

Common
All weapons that are either melee, ranged, or magical can have these mods.

Displayed values may differ due to rounding.

Melee
All Pickaxes, Hammers, Axes, Hamaxes and swung Melee Weapons can be reforged with these mods, in addition to the top two categories. The best melee prefix is Legendary.

Displayed values may differ due to rounding.

Ranged
All Bows and Guns (Excluding the Space Gun and Laser Rifle which count as Magic Weapon) can be reforged with one of the following mods, in addition to the top two categories. The best ranged prefix is Unreal. However, the Starcannon and the Clockwork Assault Rifle, while also in this category, are unable to receive any modifiers that affect knockback, as they have none. The best prefix for a ranged weapon without knockback is Demonic.

Displayed values may differ due to rounding.

Trivia

 * The Unreal status is most possibly a tribute to the Unreal Tournament games.

Magic
All Magic Weapons (mana consuming) can be reforged with one of the following mods, in addition to the top two categories. The Magical Harp lacks a Knockback value and is unable to receive mods that affect Knockback, The best choice for this is Mystic or Demonic (from the universal list). The best magic prefix is Mythical.

Displayed values may differ due to rounding.

Complete List
Displayed values may differ due to rounding.

The best mods
Each category of weapons (melee, ranged, magic, and some exceptions that are incapable of reaching the best states) has one overall best reforge. Here's an overview for them:

Accessory