Untrade-a-Box is a block which was added during the Night Of The Chemicals update. It serves as a vault for untradable items. Players can place and remove untradable items into the box, such as Growtokens or the Legendary Orb. The box cannot be traded if placed in a world or using the trade system, and cannot be dropped.
Trading the Untrade-a-Box can only be done by making it in a Chemical Combiner, smashing it and covering the item with a block, before selling the world, similar to the Zeus' Lightning Bolt. Otherwise, it cannot be traded.