Doomstone

The Doomstone is a powerful crystal formed within the chest compartment ofNemesis Prime as he (it?) travelled across the universe destroying planets, and was eventually transferred to Ravenus.

It contains the collected and condensed negative psychic energies of Nemesis Prime's victims; their pain, agony, suffering and despair. The minions of Unicronput the Doomstone into Ravenus and used his enhanced Powerlinx command to kidnap the "free" Mini-Cons Twirl and Servo, planning to use the link formed with the Powerlinx to release the Doomstone's energies into the Linkage, destroying the souls and minds of all Mini-Cons and returning them to the mindless engines of destruction they were created to be. Should the crystal be improperly handled, its energies would wipe out all life on whatever planet it was on—in this case, Earth.

The minions of Unicron were just a hair too late, though. Thanks to the intervention of Redline and Kingbolt, Ravenus was contained, and the newly-enhanced Mini-Cons were able to extract the Doomstone. Redline sealed it inside his extra-dimensional storage space to protect it from harm until they could figure out how to deal with it properly.

The Doomstone is never seen in Sailor Moon season 1, but is mentioned by Queen Beryl. The Doomstone is only seen in ''[http://sailormoon.wikia.com/wiki/Usagi%27s_Awakening!_A_Message_From_the_Distant_Past Usagi's Awakening! A Message From the Distant Past]'' and created by the Queen Metalia. Beryl possessed the Doomstone to kill her rival the Moon Princess and steal the Moonstone, but Prince Endymion managed to steal it and Princess Serenity convinced him to destroy it. Before Metalia kills Princess Serenity, Endymion crushed the Doomstone into many pieces, much to horror of  Jadeite, Nephrite, Zoisite, and Kunzite. These pieces scattered and terminated the armies.