I know
Yahenni, Undying Partisan is fun, but I don't know that you'll get your money's worth out of him with it being focused on opponents' creatures dying (and this is hard choice cut territory after all). Also personally, in the commander format, I don't see enough value in haste to run both
Lightning Greaves and
Swiftfoot Boots (especially with
Anger existing). You also do have a lot of ramp, but I see that you previously took some out, and you do probably need it with only 33 lands. I think your next card or two to take out could come from removal. If you're tempted to keep some of it as removal doubles as an alternative form of sacrifice, I think that's a trap you should avoid. You have lots of sac outlets, so you don't need removal for that. And you have enough creatures to block, and if they die, so much the better, that I think you can lose 1-2 spot removals and be ok. Also, you could, for example, remove two of your spot removal cards and replace them with one
Stronghold Assassin. It's a creature, which is good for you, and it lets you repeatedly sac a creature to kill another, which is the kind of removal that fits your commander.
As for creatures, obviously anything with ETB/LTB is helpful when you have a lot of recursion, but it looks like you're not doing as much recursion as just wanting something that is happy to die once. Undying and Persist would be great- like
Butcher Ghoul and
Pyreheart Wolf.
Nim Devourer and
Scourge of Nel Toth are great because they return from the grave AND give you more sacrifices.
Hell's Caretaker lets you swap living and dead creatures every turn.
Undead Gladiator returns from the grave and has the cycling option. Other great creatures that love to die: "egg" creatures like
Ancient Stone Idol (don't
forget it's cheat cost),
Flesh Carver,
Doomed Dissenter,
Tuktuk the Explorer,
Goblin Arsonist, and
Fireblade Charger. I also think it would be worth swapping one (or two) of your recursion cards for the really baller recursion permanents, since recursion is such a big boost to your theme. Cards like
Endless Whispers and
Grave Betrayal.
One final "mechanic" to consider- there are a lot of red cards like
Arc Runner and
Blistering Firecat that have great value for one turn with the drawback that they die at the end. That disadvantage is turned into an advantage when you have a gimmick like Sek'Kuar, so you might consider using them. I built a
Brion Stoutarm deck around cards like those. I think the ones I listed above are probably preferable, but it's an option- especially if you don't want black taking over your deck.
Two decks I'm basing this on: my Syr Konrad deck (graveyard effects/zombies) and my Marchesa deck (sacrifice/recursion). I organize them functionally like you did here, so you can pick out the effects you want pretty easily. Marchesa's getting updated, hence the massive maybeboard, but both decks have been fun to play with.
https://deckstats.net/decks/126724/1407189-syr-konrad-the-bustedhttps://deckstats.net/decks/126724/1418731-marchesa-the-playmaker