GetMouseFocus API no longer exists in any of the client flavors in the west (not sure about Asia Wrath client if that's still a thing)

Addon either needs a conditional that runs GetMouseFocus if it exists else GetMouseFoci or replacing GetMouseFocus calls with GetMouseFoci()[1]

local GetMouseFocus = function()
  if _G.GetMouseFoci then
    return _G.GetMouseFoci()[1]
  elseif _G.GetMouseFocus then
    return GetMouseFocus()
  end
end

example illustration

Even after fixing the GetMouseFocus error in my local copy though I still can't really use ShadowDancer on Cataclysm Classic.

/shd auto or shd bind only popup the confirmation static popup "Finish the operation" without the dialog I can see on addon description page.

Ctrl + left drag on a button also does not extend a flyout menu when the bar is unlocked.
No Lua errors so I'm unsure what the problem is.

I changed the logic of shd auto, when you entering that mode, move mouse over buttons, if it turn green, it means you can click it, so you can do several auto settings before you click the "finish the opeartion", for the previous version, you can do only once.

If you place a flyout spell on the actionbar, it'll auto-gen the popup bar for flyout spell, but since it's auto-generated, you can‘t drag more buttons from the popup bar.