Took some time to work out the bugs so this should be extremely stable until version 2.7 is finished ( a large update ). Please make sure your CraftBukkit or Spigot 1.9 version is up to date with /version! If it is not up to date ItemJoin may not work! Offhand support is fairly new so if you find any bugs please report them!
Added:
Added Offhand item support. Definable as slot 104:. Reference: ( 1 - 36 is main inventory. ) ( 100 - 103 are armor slots. ) ( 104 is the offhand slot. )
Fixed:
Possibly fixed all skull item lag.
Players bypassing inventory-modify prevention using the "F" key. ( Moving the item to the offhand slot ).
Skull item RIGHT_CLICK_BLOCK action not working.
Fixed the CraftItemStack dependency. ItemJoin should now work with ALL future versions of CraftBukkit/Spigot and should not break.
Fixed EntityDamagedByEntityEvent Errors.
Fixed EntityShootBowEvent Errors.
Have any ideas or requests that you would like to see in ItemJoin's future? Please submit a feature request!