Bontu seems like a fantastic late-game plan in this deck. Maybe another in the sideboard?

It did feel slightly slim/shife to only have one but was hard to balance with keeping other important things. I could see fitting another in the sideboard maybe.

I guess i will change my Black Judith, Something like this looks promissing,...

Cruel Celebrant + Judith + Priest of the Forgotten Gods is a very, very powerful deck core. Played against it several times on Arena and it's really hard to beat. Can definitely see a deck using a playset of those topping some events soon.

Figuring out which sacrifice fodder and utility cards to play is the bigger task.

I think you definitely want to play 4 Spark Harvest . It's just too good in this deck to not play 4 of it. A sac outlet and cmc 1 creature/planeswalker removal.

I'm much less convinced of Heartfire . It's not a bad card, but I think Spark Harvest is way more powerful than Heartfire. Same goes for Kaya's Ghostform .

Imo you should definitely add 1 or 2 Midnight Reaper . It's really damn good in combination with Cruel Celebrant. Costly Plunder is also an option, but I think Midnight Reaper is better in this deck.

Heartfire is a weaker choice for removal purposes. I sort of put it in more with direct damage to your opponent in mind. You're absolutely right, as far as removal, that Spark Harvest is a bargain.

Kaya's Ghostform has been useful but it is a bit of a minor side thing here.

I did skip over Midnight Reaper and you have a point about it, since Priest of Forgotten Gods can actually be a bit slow to get to use, while Midnight Reaper automatically gives you card advantage on creature death. I'd consider fitting in 2 maybe.

Thanks for the input. I still have only minimally playtested this on Arena.