Once loaded, press F3 + B (show hitboxes) and F3 + A (reload chunks). In debug mode, this combination forces a client-server resync that duplicates any item in the 9th hotbar slot.
After testing over 40 methods, the is a combination of Glitch #3 (Local File) and Glitch #1 (Wayback Machine) . eaglercraft unblocked glitch top
: Only access Eaglercraft from reputable, well-known distributions. You should never enter personal or payment information on an Eaglercraft hosting site. Once loaded, press F3 + B (show hitboxes)