This is a huge update and is definitely recommended.
With this update the plugin is considered a lot more advanced now.
Join the discord server for future updates.
You need to reset your config.yml, skills.yml and language file for this to work.

New:

• Added custom GUIs finally! Comes with new default GUI designs.
• Added "F" (switch weapons), "Q" (drop item) and "C<key>" (is a prefix for sneaking+key like CR, CL, CQ, CF) keys to combos.
• Added customizable hologram vectors.
• Added titles for level ups.
• Added armor weights.
• Added max-level for each skill.
• Added JavaScript evaluator conditions for MythicMobs level margin.
• Added required level for each ability.
• Added more options to some abilities.
• Added ability upgrade notifications when enough souls is gained.
• Added skills.actionbar permission. This permission is added by default.
• Added an option to automatically open skill selection GUI for new players.
• Added %skills_health% %skills_max_health% placeholders. You can adjust the precision in the config.
• Added %skills_max_energy%, %skills_energy_regen%, %skills_precise_energy% and %skills_max_precise_energy% placeholders.
• Added help and friends command permissions by default.
• Added an option to disable fire animation in creative. This is useful for builders.
• Added "/skill sound" command to test sounds before setting them in config. It's better than /playsound
• Added support for the latest MythicMobs.
• Added Eidolon Blackhole. First skill with the most customizable options!
• Added Eidolon Fangs.
• Added new Priest Purification Lvl.3: Crops around will grow faster.
• Added FireMage Meteorite.
• Added Devourer Consume ability.
• Added sounds to Juggernaut throw.
• Added Juggernaut Chain Smash ability.
• Juggernaut Heavy Strikes will now damage the players armor more.
• Juggernaut Stone Skin ability can now have specified modifiers for all the possible protections in skills.yml
• Juggernaut Aegis Shield will now damage the entity back for lvl 2 and knocks back if lvl 3 and under 5 healths.
• Mage heal spell ability scaling is not completely customizable.
• Mage Energy Flux can now go thro walls in level 3 and added range option.
• Mage hoe chances and damages are not customizable.
• Changed activation "cost" to "energy"
• The time placeholders format are changed to 00:00:00 This won't be the same when timer is higher than 24hrs.

Fixed:

• Fixed "Distribute Stats" option to work for skills with more than 2 stat types.
• Fixed some issues related to cross-version material support.
• Fixed "/skill user xp" adding negative XPs and not changing the level when decreasing.
• Fixed Devourer hook hurting players.
• Fixed holograms being set on fire.
• Fixed BossBar colors disappearing.
• Fixed Devourer gliders warning on disable.
• Fixed Eidolon SpiritFire error for "light" placeholder.
• Fixed missing command description for /skill statistics
• Fixed an error when trying to distribute stats with no skill selected.
• Fixed events bossbar not disappearing after the event ends.
• Fixed /skill party accept after a party is disbanded.
• Fixed Priest Passive ability keeping players flying ability after the ability is disabled.
• Fixed main scalings not supporting placeholders.
• Fixed some placeholders not loading for some messages.
• Fixed Devourer Gliders.
• Fixed Devourer Blink for 1.12
• Fixed "/skill user improve" command incorrectly limiting ability levels.
• Fixed Mage Reflect ability accidentally dealing damage to the mage...
• Fixed reload support for stats and energy from config.
• Fixed bonus placeholders.
• Fixed Boss Bars in disabled worlds.
• Fixed bonuses data serialization.
• Fixed bonuses placeholders.
• Fixed bonuses messages for /skills info.
• Fixed Priest Asclepius confusing friendly players with WorldGuard region protection.
• Fixed spelling error `charging` for Vampire blood energy type and changed default to AUTO_REVERSE.
• For 1.12 servers having issues with BossBar. There's a weird workaround that you can install PlaceholderAPI to fix the colors.

Others:

• Language file cleanup. Removed all the GUI stuff and moved actionbar properties to config.yml
• Removed cost equation from passive abilities.
• Removed unused messages from language file.
• Removed unused scalings from skills.yml
• API changes.
• Performance Improvements.