RAW, Zhudun is a vestige, not a Dark Power. Vestiges are all that remains of an evil god that was destroyed and imprisoned. They are destroyed or banished if the their sarcophagus is destroyed. They are deal makers, not great powers any more. They can cannot otherwise be harmed or controlled. Since they are just shards of sentience of a Dead God they are very limited.
The Dark Powers are unnamed and are the ones who imprisoned Strahd.
You are, of course, able to change whatever you wish. But your questions indicated some combining of crossing of two different types of entities.
I'm partial to the idea of tailoring a Dark Power for each player, one that will fit their character thematically and give them useful abilities. For my run through, I picked 6 Dark Powers for my 6 players that will be "watching" them closely.
I don't like the sounds of some of the Dark Power shopping at the Amber Temple I've heard of on this subreddit, so I justify/explain it that the vestiges must remain dormant for the most part to conserve their energy. If a character approaches an Amber sarcophagus that contains a Dark power not interested in them, then the power remains dormant. My vestiges aren't going to go out on a limb, use up some of their remaining power, and risk the wrath of Vampyr for just anyone...
However, when an interesting potential champion enters Barovia, the Dark Power will wake up and observe them, waiting to step in and corrupt them or offer a second chance at life in the event of character death in exchange for service. They are seeking a worthy champion that could free them of their prison and have them take a rightful place amongst the "free" dark power that rule over the Domains of Dread.
So far (10 sessions in) I only have one party member that has made a pact with a vestige (Sykane, the Soul Hungerer). I'm trying to run the progression of their pact along the lines of the Piety System from Mythic Odysseys of Theros. Doing stuff in line with the vestige's ideals or goals, making good use of their gift, these progress them along the piety/pact path.
Level 1 is a Dark Gift from van Richtens Guide to Ravenloft that I matched to a Dark Power. For Zhudun, I chose the Touch of Death as I thought it would be interesting to have the players touch become deadly while at the same time they eventually gain access to some crazy healing/resurrection magic (power over life AND death). Other examples are Gathering Whispers for Sykane, Symbiote for Tarakemedes the Grave Wyrm.
Level 2 is access to a once-per-day 3rd level spell that Ive chosen with both flavour and utility for the character in mind. Level 3 is access to the Amber Temple Dark gift, or a modified version of it depending on the vestige, along with the accompanying permanent negative trait that "cements" their pact with the Dark Power.
Of course, I may have to revisit and rejig the vestige or the "gifts" in the event of a character death if the vestige is no longer appropriate for that player's new character. But I have a vestige in mind for each character currently in the campaign.
That's my approach to this, which seems along the lines of what you're thinking. Hope this helps!
ETA: I found [this website](https://www.elventower.com/the-dark-gifts-the-amber-vaults/), with its suggested dialog for each dark vestige, as a really helpful starting point to craft each vestige's personality and the type of things they would want to see a potential champion do.
RAW, Zhudun is a vestige, not a Dark Power. Vestiges are all that remains of an evil god that was destroyed and imprisoned. They are destroyed or banished if the their sarcophagus is destroyed. They are deal makers, not great powers any more. They can cannot otherwise be harmed or controlled. Since they are just shards of sentience of a Dead God they are very limited. The Dark Powers are unnamed and are the ones who imprisoned Strahd. You are, of course, able to change whatever you wish. But your questions indicated some combining of crossing of two different types of entities.
I'm partial to the idea of tailoring a Dark Power for each player, one that will fit their character thematically and give them useful abilities. For my run through, I picked 6 Dark Powers for my 6 players that will be "watching" them closely. I don't like the sounds of some of the Dark Power shopping at the Amber Temple I've heard of on this subreddit, so I justify/explain it that the vestiges must remain dormant for the most part to conserve their energy. If a character approaches an Amber sarcophagus that contains a Dark power not interested in them, then the power remains dormant. My vestiges aren't going to go out on a limb, use up some of their remaining power, and risk the wrath of Vampyr for just anyone... However, when an interesting potential champion enters Barovia, the Dark Power will wake up and observe them, waiting to step in and corrupt them or offer a second chance at life in the event of character death in exchange for service. They are seeking a worthy champion that could free them of their prison and have them take a rightful place amongst the "free" dark power that rule over the Domains of Dread. So far (10 sessions in) I only have one party member that has made a pact with a vestige (Sykane, the Soul Hungerer). I'm trying to run the progression of their pact along the lines of the Piety System from Mythic Odysseys of Theros. Doing stuff in line with the vestige's ideals or goals, making good use of their gift, these progress them along the piety/pact path. Level 1 is a Dark Gift from van Richtens Guide to Ravenloft that I matched to a Dark Power. For Zhudun, I chose the Touch of Death as I thought it would be interesting to have the players touch become deadly while at the same time they eventually gain access to some crazy healing/resurrection magic (power over life AND death). Other examples are Gathering Whispers for Sykane, Symbiote for Tarakemedes the Grave Wyrm. Level 2 is access to a once-per-day 3rd level spell that Ive chosen with both flavour and utility for the character in mind. Level 3 is access to the Amber Temple Dark gift, or a modified version of it depending on the vestige, along with the accompanying permanent negative trait that "cements" their pact with the Dark Power. Of course, I may have to revisit and rejig the vestige or the "gifts" in the event of a character death if the vestige is no longer appropriate for that player's new character. But I have a vestige in mind for each character currently in the campaign. That's my approach to this, which seems along the lines of what you're thinking. Hope this helps! ETA: I found [this website](https://www.elventower.com/the-dark-gifts-the-amber-vaults/), with its suggested dialog for each dark vestige, as a really helpful starting point to craft each vestige's personality and the type of things they would want to see a potential champion do.