Also want to note that the Souless one doesn't really do much for this deck because you have Severed Legion which is nearly unblockable compared to getting Souless one blocked by an elvish visionary.
Permalink
In my opinion if a card is only one copy of itself in the deck, it is probably pulling dead weight considering the chances of you drawing it early or if it even helps at all in the middle of the game and all life gaining cards at all because it's not usual "trait" of black. I would recommend Zombie brute instead of Souless One because anyone can jump block it with a 1/1. If you really want to speed things up you should put in dark rituals and maybe a graveborn muse to spam out everything in your deck that you possibly can in like a turn or two. Try to keep it at 60 cards to maximize your chances to get the card that you need.
Instead of using the vivid lands you should use some pay lands or those eventide lands if you want some mana acceleration. The wanderwine hub looks like a bit of dead weight since you have no merfolk, but that's just my suggestion.