"A testament to the power of the person who wields it. This upgrader trumps all."
The Final Upgrader is an Ultimate-tier upgrader released in Part 2 of the 2017 Summer Update. Obtaining this item means that you have officially completed Miner's Haven, although you can still play to obtain seasonal items.
To obtain the last item of the main game, you must perform The Second Sacrifice (available at life s-1000+), and reach life S+10 to obtain this extremely overpowered upgrader. Once performing The Second Sacrifice, you will no longer be able to use The Ultimate Sacrifice. A future update will eventually bring about The Third Sacrifice.
The Final Upgrader is a buffed version of The Ultimate Sacrifice. It also possesses an ability to multiply ore value by up to x50k, assuming the same ore goes through The Final Upgrader twice.