Built with some variety of voltron, pillowfort, rattlesnake, and token strategy, just to make sure you don't put all the eggs in one basket. I had a lot of inspiration from this popular Aikido Marchesa deck, and appreciated the thought put into its strategy and contents queen-marchesa-politics-aikido-and-control Some of the ideas are stolen straight from there, some I've found to be really strong closers, such as Dark Depths and Master of Cruelties. However, without the protection that white provides in that deck, and the nature of Xantcha leans more aggressive, with some rattlesnakes and pillowforts to keep you safe.
The Voltron strategy is to play Xantcha out and steal her back, then equip. The assault suit might be the most important piece to keep her alive, to stop opponents from using a sac outlet. The rest should be mostly self explanatory. The Hero's blade would be nice to have in your opening hand for turn 2, as you get to attach it before you give Xantcha away.
It might also be prudent to find some other ways to get rid of an opponents sac outlet, there's room in the deck to replace some effects for artifact or creature removal in that case.
Using the equipment control rules are pretty beneficial in using Helm of the Host to create tokens of her, and since you control equipment on non controlled creatures, you get the tokens and divy them out to the other players (Feldon is a backup plan to this, but I'm not sure it's worth putting her into the graveyard for that effect, ymmv). With Helm of the Host, I included Godo as a backup plan infinite combat win condition when that's the only out, but people probably won't like you for that :P (Don't forget to use magnetic theft to save 4 mana to equip HotH!)
To go with the mana ability of Xantcha, I included a few enablers to do as much damage as possible, Helm of the Host, Krenko, Ashnods Altar and the token generators can probably lock out a game if you're quick about it. There's also some hand size matters type cards to take advantage of other players using the ability - Adamaro, Price of Knowledge, and Runefire trap.
Some of the ideas are more specific to my local meta, such as Dark Depths/Thief of Blood to punish counters, as well as Runeflare Trap.
There's some card draw in the form of Skullclamp, but I'm happy to add Necropotence to any black deck, the one downside is that the only lifegain is Exsanguinate.
The Myr creatures set in here is to enable a bit more consistency to the voltron strategy. As well, Master of Cruelties is a good backup voltron if you can attach some defense to him. Dread and Kazuul are in the deck for rattlesnaking, but I'm sure they work fine as well.
Some of the more expensive options can probably be replaced, Dark Depths especially so, Dread is a backup for No Mercy in many cases, and so that could easily be replaced. Price of Progress isn't so essential in the deck, and can easily be replaced, but I wanted to make sure there were a variety of ways to close out a game if necessary. Alternatively, you can lean heavily into the unlimited handsize damage if your meta has enough moments that someone has an incredible mittful of cards and aren't expecting a Runeflare trap or Sudden Impact.
Either way, I'm sure there's more tinkering to be done, as the spoiler is only one day old. Lemme know what you think could be swapped in/out or if I missed anything.
