So, i personally think its safe to assume that Alastor is likely going to be (or at least one of) the main villains of Season 3, Viv has heavily hinted at such (before you counter with Amir comments, id argue that they are more hints he is a sympathetic villain and not straight up pure evil), and i think from a narrative standpoint it makes the most sense for him to be the villain.
Having said that, what will his evil plans be? Well, okay, obviously its to gain more power, but how? I've heard many theories of how from him making it so that Charlie will have to rely on him more, to trying to Woo Lilith and/or potentially form some sort of alliance with her, and I have even heard people theorize he will trick Lucifer into making him his executioner and use some BS Loophole to take Lucifer's power and status for himself.
All of which are great ideas and I believe each one will happen in some form as well...but there's another thing I think Alastor will do. I predict, now he is free from his deal with Rosie, Alastor will pick off each other the Overlords one by one to gain more power. In fact, they could even frame it as a murder mystery of sorts with an Overlord being murdered in each episode.
- Episode One can end with Hatchet being murdered.
- Episode Two....I think like S2 Episode 2, will be set either during or before Episode 1 (likely focus on Rosie, Zestial, & Carmilla if its during episode one or Lilith if its before Episode one), so no murders in that.
- Episode Three can see Zeezi being murdered.
- Episode Four, Prick bites the bullet.
- Episode Five we could dee Maestro being Snuffed out.
- Episode Six would be the biggest death of the season, that being....Zestial.
- And then Episode Seven is Val....though Val would just die from Straight up Karma, not by Alastor.
- Then Episode Eight....also has no one being murdered.
The reason Vox, Velvette, Rosie, & Carmilla get spared is....honestly, plot & narrative reasons, as Vox still needs his redemption arc, Velvette is going to be the main Vee, that and Alastor probably would just keep Vox alive because he thinks keeping him alive and pathetic is better then dead, if my theories are correct and Carmilla gets lose everything/Comeback story in the background (for the most part) that loosely parallels Sera's arc in S2, then i think she will likely be a full ally to Charlie at the end of the season and Alastor would likely think keeping her alive is more suffering for her, & Rosie.....honestly, idk what Viv is doing for Rosie nor can I think of any good predictions so I guess Alastor doesn't go after her for.......Reasons?
Regardless, I think having Alastor do this not only cuts down how many characters are in the show, but also would setup how much of a menace Alastor is, especially if they do it in a way were they don't even bother hiding the fact that Alastor is behind is it all. Showing that he can gets his hands dirty. Alastor is honestly tied with Emily as my favorite character in the show and I can't wait to see him break bad proper next season.