Cosmic Crucible

Cosmic Crucibles are unique devices that can upgrade items far beyond their normal stats. They can be found in Precursor microdungeons, in the Precursor Ruins mission, and in the Science Outpost (through a 1-block gap at the base of the cliff on the left).

Weapons can be improved from level 1 up to level 8.

Updated as of v5.6.347

The Cosmic Crucible and the tiles below it are impervious to any attempts to remove it. If you somehow remove the Cosmic Crucible, nothing will drop (not even the anvil).

Fake Cosmic Crucible
There is also a fake Cosmic Crucible which is rigged with instakilling bees (that can also bypass admin mode) by Kevin. When attempting to place the item down, it will disappear from the player's inventory, and release the bees inside.

The rigged version is inaccessible by normal means, and can be only spawned in