First off, it has flash, so you can drop it at just the right moment and immediately shrink a creature by -4/-4, potentially taking out a key threat
The strategy for a deck with Zhulodok, Void Gorger is far different than Omarthis, so many of the cards in the precon stray from Zhulodoks main strategy
The issue is that there is not enough of the generally playable one mana options for one person, let alone two people in the colour, not that there are not enough total to have black fully covered for its potential needs in the discard department
The Swamp is the best of the cycle, showing the black mana symbol being slowly drenched in ichor, as two avatars of death look on from the sides
The overpowered (and banned/restricted) blue card Ancestral Recall is also part of this cycle, as is the distinctly underwhelming white Healing Salve
Biogenic Ooze is an old combo deck using creature cards in the grave, but now with Trazyn, he can be your commander and instead wants artifacts