v2.0.0:
Notes:

• Before installing this update, you must read the 'Important' section below. The plugin WILL malfunction if you refuse to follow the information provided there.
• I wish to start off with a huge thank you to stumper66 for their massive list of contributions this update. Stumper also gave me the spark to recontinue work on the resource. This update wouldn't be here without him!
• I've recontinued work on the plugin. Most of the code has been updated from the previous version. This update took so many hours to make, so I really hope you all like it. 7 other people assisted stumper and I to get this update through.
• (psst: leave a like / positive review if you enjoy this update!)

Important:
Before installing this update on your server, please understand the following:

• Nametags now require ProtocolLib. If you do not install ProtocolLib, then you will not see levelled mobs' nametags.
• PhantomLib is no longer used by LevelledMobs. Uninstall it if you wish (unless you have other plugins that depend on it installed)
• Every single permission has changed, and a bunch have been added in too. I recommend you remove any current permissions from LM you have set to your groups and apply the new ones. See the documentation.
• If you are using any WorldGuard flags from this plugin, you should remove them from your regions prior to installing this new version. ALL previous LevelledMobs flags have been renamed, and I've also added in a new flag which was a popular request.
• Reset your config! You might want to back it up in case you want to copy old settings across, but the settings file has changed enough that I would recommend starting from scratch.

Impossible without the collective help from:

• @stumper66, whose contributions are too many to list here
• @CoolBoy, @Esophose and @7smile7 for creating & fixing the complicated packet nametag method
• @Oathkeeper for their great feature suggestions and testing
• Hugo5551 for making a handful of great code suggestions
• squeebis for helping us out with testing
• JacksaYT for reporting multiple bugs, some of high importance

Changelog:
Summon Subcommand (stumper66)

• The summon command is finally complete thanks to efforts by stumper66!
• Summon the specified level, amount of mobs and at your location, another player's or an x/y/z location.
• Added setting 'summon-command-spawn-distance-from-player` with default of 5.

Kill Subcommands (stumper66)

• The KillAll subcommand has been revamped and split into two subcommands; kill all [world] and kill near [radius]. (stumper66)
• Now kills mobs instead of instantly removing them. This means drops, exp, etc. (stumper66)
• <world> argument accepts a wildcard (* character) to specify 'all worlds loaded on the server' to have levelled mobs purged from.
• Now checks for new entity NBT 'isLevelled' to kill the mob. (lokka30)
  • This means that mobs that were previously considered levellable will also be killed.
  • This means that mobs that are not levelled but now considered levellable will not not be killed.

WorldGuard Flag Changes and Fixes

• Added a new flag 'LM_AllowLevelledMobs': deny this flag to tell LevelledMobs not to level a mob that spawns in a region. (lokka30)
• Renamed the old flags. The renamed flags are:
  • 'LM_UseCustomLevels': this determines if the custom min and custom max level limit flags are in effect. (lokka30)
  • 'LM_CustomMinLevel' and 'LM_CustomMaxLevel' put a boundary on how high and/or low a mob's level will be if they spawn in the region. (lokka30)
• WorldGuard flags were broken, we are unsure for how long this was the case. Luckily it was a simple fix. (stumper66)
• WorldGuard level restrictions now properly respect the max level if both max and min levels are set to the same value. (stumper66)

New Powerful Permissions (lokka30)

• With all the new features finding their way into LevelledMobs, it was becoming necessary to restructure the permissions.
• Almost all permissions have changed, and a bunch have been added.
• Full wildcard support (* character, e.g. levelledmobs.command.*) to make applying permissions far quicker.
• The command now requires a permission to run too (given by default) in case you wanted to restrict access to it.

Packet Nametags (lokka30, CoolBoy, Esophose, 7smile7, stumper66)

• This feature requires ProtocolLib to be installed, else the LevelledMobs nametag system won't be enabled.
• No longer does LevelledMobs mess with nametags! It instead modifies the packets sent to the client.
• In other words, LM sends a 'fake nametag' to the client, but there isn't actually a nametag on the mob.
• This has fixed the following problems:
  • You can now apply nametags to levelled mobs without losing the levelled nametag
  • Anti-lag plugins usually ignore nametagged mobs - this means they will now kill levelled mobs too, since there isn't actually a nametag on the entity.
  • Essentials' killall command now works properly!
• This was possible thanks to help from @CoolBoy, @Esophose and @7smile7 in this thread. A big thank you to them for their assistance.
• Thanks to @stumper66 for assisting me with band-aiding issues caused by this new system.

Full Tab Auto-Completion Implemented (stumper66)

• The commands now feature full auto tab-completion to help speed things up.

Bye bye, PhantomLib (lokka30)

• I have made the switch to my new development library, MicroLib.
• Server owners do not need to install MicroLib as it is embedded inside of the LevelledMobs plugin file. It is also not a separate plugin, rather part of this plugin.
• Server owners are recommended to remove PhantomLib if it is no longer used by any of their installed plugins as it will remain unsupported.

Y-Coordinate Levelling (stumper66)

• A brilliant suggestion by @Oathkeeper, this levels entities depending on their y-coordinate. It functions very similarly to 'distance from spawn levelling'.
• This can make mining in caves that much harder!

Creeper Blast Radius Scaling (stumper66)

• Creeper blast radius is now scaled with their corresponding level.
• The amount is configurable in settings. Default is 5 for max blast radius (vanilla creeper radius is 3)

Configurable Chat Messages (lokka30)

• Added a messages.yml configuration file, in which server owners can now translate all chat messages from the plugin i.e. those sent from the command.
• Generic colour code support (no rgb yet).
• Multi-line support.
• %prefix% variable available on all messages.

Default Level Nametags (stumper66)

• New setting to apply nametags on default leveled mobs.
• If set to false and a level 1 mob is spawned, no nametag will be applied to the mob.
• This gives a more vanilla feel.

New Additions System (lokka30)

• Replacing the old "multipliers" system that didn't actually function as a multiplier, introducing the Additions system!
• For each level a mob has, the 'addition values' will be added to their attributes, e.g. movement speed.
• It is highly recommended that you don't touch anything in the fine-tuning section since the numbers are pretty sensitive.
• The default addition values have been properly tested, unlike the previous multipliers which were beyond hardcore

New Attributes System (lokka30)

• LM now stores a pregenerated attributes file in its data folder. This contains all of the default attributes for every living entity in 1.16.
• This file will be updated with each new Minecraft version.
• This will improve compatibility with plugins such as SafariNets immensely.
• A secret, secure command has been implemented (only accessible by console with a password) which generates a new copy of the file. This is only meant to be used by developers. It is used to update the file with new Minecraft versions.

Entity Transformation Fixes (lokka30 + stumper66)

• All entities that transform into other entities (e.g. Zombies->Drowned and Slimes) now carry over their parent's level.

Other Bugfixes

• Magma Cubes, Slimes, Ghasts, Phantoms, Ender Dragons, Shulkers and Hoglins are now levelled as expected (stumper66)
• Armor Stands no longer have items/xp drops from death multiplied (lokka30)
• XP drop management now checks if the mob is levelled rather than is levellable, fixes possible NPE (lokka30)
• Many unwritten bugs fixed by stumper66 and lokka30 during the pre-release testing stage

Removed Features

• Removed an old feature 'flight speed multiplier' which we found out Minecraft only applies to parrots. Completely unnecessary and misleading. (lokka30)
• Removed 'default attack damage increase' (lokka30)
• Removed 'remove nametag on death' which is no longer necessary with the introduction of packet nametags. (lokka30)
• Removed 'update nametag on health update' as LM does this automatically (stumper66)

Other Code Changes

• Cleaned up the every single class in this project significantly. A bunch of methods and variables have been moved to more fitting classes too. (lokka30)
• Removed the LightningStorage system - it has been replaced with a far simpler system. This will not only increase performance, but also decrease clutter in the code and decrease the file size of the plugin. (lokka30)
• Moved all subcommands to their own classes implementing a Subcommand interface - cleans up the LevelledMobsCommand class to a huge degree (lokka30)
• Added LevelManager#isLevellable(EntityType) so a mob can be checked if it is levellable or not before it spawns in. (used in the summon command) (lokka30)
• Added the ListMode enum which will make checking lists in the config easier and cleaner (lokka30)
• Added all code contributors to the 'info' subcommand. (lokka30)
• Use HashSet for forced entity types instead (Hugo5551)
• Determine level after the entity is deemed levellable (Hugo5551)
• Removed sound from debug feature - in case older versions become supported, this sound will need to go anyways (lokka30)
• Rearranged the Manager classes from the utils package to the main package (lokka30)
• Use (ignoreCancelled = true, priority = EventPriority.MONITOR) with most event handlers (Hugo5551)
• Improvements to the debug listener (stumper66)
• Improved compatibility checker (lokka30)