you definitley need
Black Sun's Zenith! Best card in this deck.
I also play
Dusk Urchins as carddraw (could work very nicely with your
Channeler Initiate). Play
Carnifex Demon as an endless -1/-1 counter engine with
Blowfly Infestation. The last creature dying lays its counter back on the
demon so you can repeat - awesome, you'll love it. Suggest
Serrated Biskelion as an alternative card to
Serrated Arrows. As fast as the arrows, but lays 4 counters instead of 3, two at a time. Also works better with your
Zulaport Cutthroat. Also suggest
Putrefy rather than your other two removals.
Quillspike is nice but not needed, since you get
profit from every creature that dies with an counter. Don't ever cut
Blowfly Infestation, since it's your epic CC card on the battlefield.
Crumbling Ashes looks really nice, but shouldn't also be needed if youre flooding the battlefield with your counters.
Noxious Hatchling is a nice fatty, but sadly doesn't do anything for your goal.
Also very sadly, your best combo engine of this deck (
Nest of Scarabs &
Blowfly Infestation) can also be your worst enemy, since it creates an infinite loop, if no creature on the battlefield is stronger than 1/1, because none of the effects is optional.
I also suggested
Kulrath Knight, sady its CMC are much too high since you can't be sure it will control all of your opponents creatures.