Compared to aggro spirits, this list is lacking in synergy. This deck really, really wants to fit Bilious Skulldweller, but I can't reliable experiment with splashing black, simply because across several options, the manabase always behaves differently. (Arena, tappedout, and mtgduelist)
Without the Skulldweller, there is a slight lack of aggressiveness that puts this deck behind the already existing lists it's competing with, mainly that you could end up with Ivy, Gleeful Spellthief, Hope of Ghirapur, and a lone Wasteland Viper for your first couple of turns. There are several ways of potentially fixing this, but they require more practical testing. Now I know every decks' weakness is a bad hand, but in this case it still borders a lack of consistency, especially to satisfy what should be a competitive contender.
This decks manabase could easily go down to 19, but I've left it at 20 because of the already mentioned inconsistencies with my draws during testing.
Finally, in pioneer, the Rotpriest is not enough to do away with toxic/infects issues of old. There is a lot of fodder for debating on why to go for poison counters and not just, you know, stick with reducing your opponents life total to zero. If you want to go with this strategy, and actually commit to it, you need to outspeed those other aspects, or poison counters become pointless.
But enough negatives, when you do hit that 60%-70% hand however, there is not much able to stop you from going in regardless of what your opponent is doing, except exile and -x/-x effects. In case of those becoming more relevant in the meta, more Slip Out the Back is your best friend. I have not missed a single discounted Distorted Curiosity in my playtests and even losing a Rotpriest or Fynn, you reload quickly. The big reason to play this over other aggressive strategies, is the fact that you don't need to buff, hold, love or smell your creatures, you just need to attack with them three to four times.
In other words: the strength over other decks is our ability to entirely focus on turning everything unblockable, protecting it, or otherwise disrupt our opponent and prevent them as much as possible from playing the game they enj- I guess the Ichor is setting in. Hail Phyrexia!
