The Death-X, also known as "The Evolution of Death" (「死の進化」), is an old relic of evolutionary research that artificially increases the survival instinct to its limit, causing a digimon to overcome the very concept of mortality by incorporating other digicores to its own, making the digimon undergo an special type of evolution known as "Death-X-Evolution".
During the first execution of Project Ark in 2003 D.C., Yggdrasill awakened the Death-X from the depths of its storage to effectively erase the digimon it wanted to be deleted. However, the Death-X became "a dangerous program that is not a Digimon: Death-X-mon" (「デジモンではない危険なプログラム：デクスモン」), which only devours digicores as a zombie.
After it had ordered Magnamon of the Royal Knights to captures DORUgamon and bring him to it, Yggdrasill analyzed DORUgamon's data and created Death-X-DORUgoramon from it. From there, Death-X DORUgoramon created hundreds of digitama containing Death-X-DORUguremon. It was later confronted by Alphamon and Omegamon when it was summoned by Yggdrasill. Although Omegamon barely hurt it, Alphamon easily destroyed it with a single attack. It was later revived by Yggdrasill as Death-X-mon to defend it. After their attacks seemed to be innefective, Alphamon realizes how to defeat it and impales both himself and Death-X-mon with his sword, telling Omegamon that it was the only way, because Death-X-mon is his shadow and that if he didn't have his friends, he may have turned out like him.
When Omegamon X defeated DORUgoramon it forces him to evolve into Death-X-DORUgoramon. Unable to defeat it, Omegamon X is able to separate the Death-X data from DORUmon, and expelled it from the New Digital World. Yggdrasill retrieved this data and unleashed it into the Skuld Terminal, where it became Death-X-mon. Omegamon X faced Death-X-mon but was unable to defeat it, as Death-X-mon was unaffected by his strongest attack, "All Delete". Eventually, Alphamon and Ouryumon went to the Skuld Terminal to face Death-X-mon. While Ouryumon was killed by Death-X-mon, Alphamon was able to use his data to evolve into Alphamon: Ouryuken and defeats it.
Death-X-mon is a main antagonist in the Lament of the X-Antibody chapter (慟哭のＸ抗体編 Dōkoku no X-Kōtai-hen). In order to fight the protagonists in the Infinity Mountain, Yggdrasill takes control of DORUguremon and forces him to evolve into Death-X-mon. It can only be obtained as a collectible card. Its card can be unlocked when completing the Death-X-Evolution (デクスリューション Dekusuryūshon) set and is part of the X-Antibody of Destiny (運命のＸ抗体 Unmei no X Kōtai) set.
Can be obtained as a Blast Evolution of Alphamon: Ouryuken.