Doomstone

The Doomstone is a powerful crystal formed within the chest compartment of Nemesis 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 Unicron put 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 created by the Queen Metalia. Unlike the Moonstone, created by Queen Serenity, which can grant anyone's wishes and desires, the Doomstone has the power to curse anyone. A long time ago, Queen Beryl possessed the Doomstone to kill her rival the Moon Princess, 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. These pieces scattered and terminated the armies.

Beryl recreated the Doomstone after 10,000 years. She used its power to seal Jadeite into Eternal Sleep for his failure and kill Zoisite as a punishment. The Doomstone made its last appearance in the final episode of Sailor Moon Season One when Sakura stolen it and saved Sailor Moon by blocking Endymion with The Sword, who was brainwashed by Queen Beryl. When Beryl demands Sakura to give back the Doomstone to her, the Cardcaptor threw the jewel to the ground, shattering it into pieces which crumble into dust, never to be seen again.