As anyone who's started porting to 1.14.2 is probably aware by now, container and GUI creation has changed... quite a bit.  To summarise what I've gathered so far: Containers (more accurately: container types) are now registry objects and must be registered in a RegistryEvent.Register<ContainerType<?>> event handler. Container objects themselves must provide a constructor of the form MyContainer(int windowId, PlayerInventory inv, PacketBuffer extraData).  This will be us