I’ve seen the base-Sultai lists and they’re interesting, but you lose a lot of speed going from Voice to Charm. There’s a reason that I’m not already running four Scout the Borders, which is arguably stronger for this deck than Sultai Charm. I also have had very little trouble casting Sagu Mauler with the current configuration, while I could see getting all five colors being a bit more difficult for the sultai-based shell. It’s something to consider, but I haven’t seen a good list of Sultai yet and I haven’t been able to configure one myself either.

The Debilitating Injury kind of started as a joke, but then it just really worked with the deck. Being able to Commune for it is marginal upside, but it’s more for the fact that you want to be able to cast it on turn two and double black isn’t always a given. It could very well be better as Downfall or Blight, but I haven’t really found myself wanting for them. If I changed it to either it would be the blight, as killing something like double Monastery Swiftspear or Gobling Rabblemaster at instant speed would be great here. Downfall I don’t like as much, as we already do very well against large creatures and the planeswalkers that are good against us mostly do their damage on their first activation- Elspeth, Ugin, Liliana… It’s random upside against Ashiok, but that’s a very low impact plan against a bad matchup.

Also, I don’t understand your choice of Debilitating Injury for the sideboard. I know you want it for speed and because Commune can pick it up, but wouldn’t it be better as a Bile Blight or Hero’s Downfall?