• By default, weapons can't level up; the mechanic must be activated via. items called Experience Runes, using an Experience Rune Forge (See their sections below)
  
• Weapons that can gain XP will do so whenever they deal damage. In most cases XP gained is equal to damage dealt
  
• Bosses, events, and worms all have multipliers which reduce the XP granted when fighting them, to combat power-leveling
  
• The XP required to level up is calculated dynamically based on level; as a weapon levels up, its XP requirements will steadily become greater
  
• Weapons will gain a damage boost as they level up. It starts very small, but will add up with each level
  
• By default, the max level is 100, at which point weapons receive x3 damage

• This is a special crafting station that is the core of Experience Rune/Orb management
  
• Crafted from a Furnace & 3 Fallen Stars
  
• ALL recipes in the mod utilize this crafting stations
  
• Right click a placed Forge to open its UI, which facilitates applying Experience Runes/Orbs to weapons
  
• The Forge UI's 'Apply' button will display tooltips when hovered over, providing feedback on required items and/or incompatibilities

• These are craftable items which activate a weapon's ability to gain XP and level up
  
• All Runes' crafting stems from the Dormant Experience Rune, craft one with 5 stone and a gem at an Experience Rune Forge to get started
  
• Different Runes apply different 'Base XP' values to weapons, determining how easy or hard it is to gain levels
  
• A weapon's Base XP is how much XP it needs to get from level 0 to level 1. This value is used to calculate all level thresholds
  
• A weapon's rarity will dictate what tiers of Rune can be applied to it, with higher rarities requiring higher tiers
  
• Higher tier Runes require materials from later in the game's progression, and apply higher Base XPs

Ethereal Runes

• These are an additional, special, easily-accessed counterpart that work on any weapon.
  
• Ethereal Runes are ideal for bypassing progression and other barriers to suit your own tastes for balancing
  
• Ethereal Runes are also useful for weapons with modded rarities, since they default to the highest Rune tier

These are special items that rarely drop from enemies and can be used to bolster your weapon's training by instantly granting a dynamically calculated amount of XP

• XP granted by an orb dependents on its type/size and the base XP of the weapon it's applied to
  
• There are 5 rarities of orb, with the rarer variants being stronger
  
• There is also a sixth, special type which instead grants a single level to a weapon
  
• Orbs can be crafted into counterparts which deduct XP, if you ever find a need to do that...

An optional addition that allows your player to level up as well

• Players' ability to gain XP is inherent and not dependent on Runes
  
• Player level can also confer a (global) damage boost, though it is much smaller and is turned off by default
  
• Likewise, there is also an optional boost to damage reduction from player level, also disabled by default
  
• Both of the two above features are not recommended for balanced play
  
• A Reflection Rune can be used to view your player stats. One is given to newly created characters, or it can be obtained by throwing a Dormant Experience Rune into Shimmer.

There are a few items in the mod that can help you with grinding XP, though some come with drawbacks in return

• The Reflection Rune can be turned into the Effort Rune at a Demon Altar. This version can be equipped as an accessory which reduces your defenses and mobility in return for boosting XP gains
  
• As an alternative to directly using them for instant XP, Experience Orbs can be brewed into Training Potions which temporarily boost XP gains
  
• Mystic Experience Orbs can alternatively be used to craft the Challenge Totem, which can be placed down and activated to boost XP gains in return for reducing player damage
  
• The Skeleton Merchant sells a new accessory, the XP Tithe. When equipped, it reduces XP gains, but makes Experience Orbs much more common in return

Want to take your player or weapons farther than otherwise allowed? With Prestige you can do just that;

• Buy Prestige Runes from the Travelling Merchant in order to Prestige a level 100 player or weapon
  
• Prestige will wipe the player/weapon's XP and reset it to level 0, but preserve the damage boost gained from the previous levels
  
• This allows you to keep gaining more damage from further levels!
  
• However, it is very difficult to level up Prestige players/weapons; weapons gain XP 20 times slower, and players gain XP 50 times slower!
  
• If your Prestige weapon reaches level 100 again, there is a config option that allows stacking Prestige; up to a max of 3 times!
  
• Stacking Prestige offers even more power, but also makes gaining XP exponentially harder.

Note that Prestige is rather overpowered in nature, so it isn't recommended to use unless you don't care if it's unbalanced and/or are just interested in power.

Another optional feature that allows enemies to gain extra HP and Defense as you progress

• When enabled (The feature is off by default), enemies gain up to x3 HP and x1.5 Defense based on downed vanilla bosses
  
• This feature will encourage you to spend time leveling up weapons in order to keep up with increasingly resilient foes
  
• To reduce the increased amount of grinding, XP gains are greatly increased when this feature is active
  
• Enemy stat scaling, and bonus XP can be customized via. config

Yet another optional feature that enables a dynamic level cap that must be raised as you progress

• When enabled (The feature is off by default), weapons/players have a level cap of 10 by default
  
• Most vanilla bosses will drop new Medal items when defeated. These are permanent consumables that raise the level cap by 5-10 levels
  
• A given Medal type can only be used once. Keep hunting down bosses to raise the level cap as you play!

If you actually read through all of this, I salute you. Thank you for being a literate member of the tML community!