Jewel of Mystery

The Jewel of Mystery (神秘の宝玉 Shinpi no Hōgyoku, aka Gem of Mystery) is a jewel holding great power that was left behind on the planet Zel Samine by the Lazalt aliens long ago.

The Transformers (PS2)
The Lazalt Ruins in which the Jewel of Mystery rested were discovered by the people of the Paradius solar system shortly before the arrival of the Transformers on Zel Samine. Both the Autobots and Decepticons figured the jewel was a good candidate for the Zel Quartz they were searching for and set out to get it. After a big clash over the jewel, the victorious party brought it back to base, where it was discovered that, no, the Jewel of Mystery and the Zel Quartz were not the same. In case the Autobots got their hands on the jewel, they returned it to the Lazalt Ruins. In the other scenario, the Decepticons kept it.

Ask Vector Prime
In one of the many variations of Primax 1003.30 Kappa, Dirge encountered the Gem of Mystery and was blasted into unspace. Unicron subsequently plucked him from the void, adding him to his roster of Heralds.