Beta Item
The Beta Item (unofficially named so for the β on its surface, the actual in-game name for it is 0) is not supposed to be obtainable,
When stored, the item disappears completely, however it can be carried between levels. It may be a placeholder in the inventory for a lack of an item, given that empty inventory slots share its ID.
When released, the item rises upwards indefinitely, passing through all blocks in its way, though it does stop when in water, is sped up in lava, and can be redirected by explosions. A player skilled enough at using it could pull off incredible maneuvers, easily gliding up the tower, so long as they are careful to not let it fly away.
Obtaining
The Beta Item is created when two items are spawned on the same frame (e.g., destroying two wasp hives on the same tile) The easiest way to get it is to plant 2 Seeds at the same time, which can be achieved by throwing a seed upwards, then throwing the other one downwards as the first is about to land.