When it comes to speed, your 4-slot is incredibly heavy, way to heavy
(As it sucks souls, this may represent your increased power as the game goes on.) Here are some quick brainstorm ways (that may not work if play-tested, or at that three mana cost) that would have been Blackbladed
Ghoulcaller Gisa creates explosive boards from just one creature by converting power into Zombie tokens
He had stored it in two ways: the best specimens were preserved in binders, while others remained unsorted in a tin
Then I tried a variety of sideboard cards with some being dead awful (looking at you Wasteland and Dust Bowl) and some being kinda ok, like 4 Living Death and Null Rod
Hazezon, you served us well as a primer on how to brew a Desert deck