Ammit Eternal has impressed me. A 5/5 for only is pretty efficient, and the Afflict mechanic is interesting. I sincerely thought about this main deck, but I think Ruin Raider is better, and I don't want too many 3+ mana creatures main because of Ruin Raider.
Duress is good, particularly against control, for eliminating pesky removal spells and planeswalkers. Good card to disrupt a player's game.
Harsh Scrutiny, like Duress, is great for messing with a player's game plan. It is particularly effective when there are larger creature threats (e.g., The Scarab God, Hazoret the Fervent, Glorybringer, Bristling Hydra, to name a few great targets).
Kitesail Freebooter is a good card. I don't use it much, but against a God-Pharaoh's Gift deck, it seems to be quite useful for removing Settle the Wreckage and God-Pharaoh's Gift. It is subject to removal, so it really takes the correct matchup for it to be impactful, though the flying is certainly a plus!
Never / Return is not as common in these mono-black decks, but I prefer it to Bontu's Last Reckoning as it can use the Return part of the card (so, 2 spells in 1 card) to eliminate important graveyard targets (e.g., The Scarab God, Angel of Invention). The ability to hit a planeswalker or creature is also quite nice.
Vraska's Contempt is just good removal, albeit 1 more mana than I really want to pay. Nevertheless, I also gain 2 life and exile a powerful creature. Can't complain too much.
Walk the Plank was in the main deck, but I replaced it with 4x Dire Fleet Poisoner. Here's the text from when it was in the main:
Walk the Plank is good for the larger creatures. After sideboarding, it is great to couple with the Return part of Never / Return to exile The Scarab God or a similar threat. It's also good for killing many of the annoying creatures of Temur/4 Color/Sultai Energy (e.g., gearhulks) and Ramunap Red (e.g., Glorybringer).
Ruin Raider was in the main but replaced with Dusk Legion Zealot. This is only an experiment. I am moving the Ruin Raider text to here until I decide whether to keep it or not.
Ruin Raider is a card that I simply didn't get when it was first spoiled. However, after having played with the card fro a while, I now understand how powerful it can be. In a low-to-the-ground deck like this, the damage from drawing cards is generally negligible, and the lifelink often makes up for it. The card advantage is amazing. Good card. It is also often sided out to make room for Vraska's Contempt, Ammit Eternal, and/or Never / Return because adding more cards with higher mana cost can start to make Ruin Raider a liability. However, being able to crew Heart of Kiran and to provide card advantage is worth it.