Runes

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Runes is a datapack that adds 21 runes to find, ranging anywhere from health boost runes to respiration runes.
They come in 5 rarities, common to legendary, but not every rune is available on every rarity.
Runes can be found in many different places, so lets go over them all

Common runes can be dropped by hostile mobs, having a 1/15 chance
Uncommon and Rare runes can be found from chests, having a 1/4 chance to contain a rune, with the rare runes being rarer of course
Epic runes can be dropped by boss mobs (ender dragon, wither, elder guardian, warden) and has a 50% chance to drop.
Legendary runes are 1 time rewards for completing certain advancements, there are 4 advancements that count, but I'll let you figure out which ones those are.

Now that you know where to find runes, what do you do with them? Well you can equip them in your brand new runes menu of course.
The runes menu can be opened using the playerlist key (default: tab, sneak to view playerlist again), there you will find 7 rune slots, 2 offensive, 2 defensive, 2 supportive, and one accepting all runes.
Just put a rune in a corresponding rune slot to reap the benefits of the rune. Runes of the same type can stack (except for haste and night vision) to achieve even greater effects.

This is a new hidden layer so this will apply to all players.

While not explicitly required, it is highly recommended to use the runes resourcepack for better visual clarity.

Happy rune hunting!