Copy shape keys

Don't you copy a shape key by turning them all to zero except the one you want to copy (which you set to 100%) then use "New Shape Key from Mix" ?

I also have to say, it's not quite right that there's no way of copying shape keys. select the object from which you wanna copy, select the shapekey you want to be copied, then Shift-Select the target object and in the shape keys press the downlooking arrow to open up context menu and then choose "transfer shape keys".... This is completely out of my head but I'm pretty sure I was able to copy single shape keys around like this. The one thing that also has to be made clear here is if you're talking about identical meshes or not.

for everyone trying to copy ALL shape keys between two IDENTICAL objects, select first the source object, then the target and run following script, found on below website: reddit.com/r/blender/comments/er7sw4/copy_all_shape_keys_from_one_object_to_another/

import bpy

def copy_all_shape_keys():
    if len(bpy.context.selected_objects) == 2:
        source = bpy.context.selected_objects[1]
        dest = bpy.context.active_object
        for v in bpy.context.selected_objects:
            if v is not dest:
                source = v
                break

        print("Source: ", source.name)
        print("Destination: ", dest.name)

        if source.data.shape_keys is None:
            print("Source object has no shape keys!") 
        else:
            for idx in range(1, len(source.data.shape_keys.key_blocks)):
                source.active_shape_key_index = idx
                print("Copying Shape Key - ", source.active_shape_key.name)
                bpy.ops.object.shape_key_transfer()

print("Start")
copy_all_shape_keys()
print("End") 

;)

1.select your destination shape key (it should be a copy of the basis), then go into 'edit mode'

2.select the vertices you want to move

3.press [ctrl]+[V] and 'blend from shape'

4.press [F6] or look at the bottom of the [T] tool shelf for the context menu, change the key to the 'source' shape key you want to copy from. If you are not working from 'basis' you may need to adjust the 'blend' to better match the shape key you are blending from.

You can base a shape key of another one - can't remember exact terminology. Not sure if this helps your scenario or not.