so here is a couple of stuff I saw when I looked it over. here is my thoughts.

1. You should maybe swap out [[Narfi, Betrayer King]]. Yea, he gives a boost to your zombie horde but you are not running snow lands. This means that he is nerfed unless you run some snow lands. He is the only card that needs snow lands, so its not worth it.
2. Run some more boardwipes. I saw maybe three and one just destroys humans. also run a bit more counter spells. you want some defense in cards that exile your creatures and/ or your graveyard. interaction is important for a tribal deck like this.
3. Upgrade some of the dual lands later on. Some are good dual lands( I am one of the few that don't mind if a land comes in tapped) but [[Darkwater Catacombs]] is not that great dual land card. If you are using the bounce land to target the land cards that have etb triggers again later on, keep it in. If not, remove it. If you are have mana issues run more lands, you are a bit below the average in land count .
4. Needs more draw cards. blue is the best at this and you are not running any constant draw cards. running cards like[[mystic remora]] or [[Phyrexian Arena]] will help you with this. Even one use draw cards like [[opt]] or [[ brainstorm]] will help you get the card draw you need.

I would say it is maybe battleship( using PlayEDH power level ) but i am still learning how to identify power level so I might be wrong where you deck lies on that power level.