Make sure you update ProtocolLib to 3.7.0-SNAPSHOT. Make sure your Spigot build is the latest and greatest available.
There are a LOT of changes in this version, please pay attention:

Plugin changes:
- 1.9 support has been added
- Fixed the datawatcher
- All disguises function in 1.9
- Added the Shulker Disguise
- Added the Area Effect Cloud Disguise
- Updated all animations for Zombies, Skeletons, etc.
- Fixed the bed animation
- Fixed nametags not appearing above mobs
- Fixed enderdragon positions
- New config option:

#Stop shulker disguises from moving, they're weird. This option only effects PLAYERS that are disguised, other entities disguised as shulkers will NOT be effected!

StopShulkerDisguisesFromMoving: true


API Changes:
- DisguiseWatchers now have appropriate methods of MainHand and OffHand
- Disguises no longer use ItemStack[] arrays, but EntityEquipment
- More methods in disguise watchers for various options


Upcoming Changes (Not implemented yet) :
- Sounds will be re-added shortly in the future
- Player elytra animation is missing, will be added
- Boat and Shulker Watchers are missing certain options, will be added


Full list of changes available on GitHub: https://github.com/libraryaddict/LibsDisguises/issues/98

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For Spigot Version: 1.9 and higher

ProtocolLib version: 3.7.0-SNAPSHOT