MrShulker is a recreation of the core features of the (assumed abandoned) Shulker+ Mod.
The mod allows players to attach items to shulker boxes for 1 xp using an anvil. The attached item then displays on the lid of the shulker box.
The mod is required server side. It is optional client side. Items can be attached to shulkers with or without the mod installed client side, but it is required for the lid items to be displayed.
as of version 1.3.0 Mr Shulker now supports dyeing of shulker boxes by using dye on them provided by tnoctua.
MrShulker is backward compatible with Shulker+, If you are migrating from a world which had Shulker+, you need to have MrShulker installed at the time of migration for the data to carry over.
External resources
Project members

mr.mindor
Owner

tnoctua
Contributor