spoiler thoughts in no particular order:
The theme of this season seems to be "replacement." Characters are constantly taking on other character's roles. Heimerdinger highlights that Jayce is his former pupil and Ekko is his new pupil. Jinx acquires a Powder-esque kid sidekick and finds herself in Vi's role, while Vi finds herself hurt and abandoned by someone she loves most in a very Powder-y position. Caitlyn struggles to replace her mother, and Ambessa very tactically places herself in that authoritative role to give Caitlyn the motherly guidance she no longer has - essentially replacing Mel in the process. Everyone is being shuffled around, and very few of them are taking it well.
It's interesting to me that, amidst all this replacing, two roles are conspicuously not being filled: Silko and Vander. Silko's death has left a gaping wound in Jinx and Sevika's operation, and neither of them are attempting to replace him - instead, they're trying to figure out their dynamic without him between them. In a strange way, it feels like Jinx is maturing. She's beginning to recognize that she doesn't actually destroy everything she touches; there are things in this world she CAN fix. This is extremely un-Silko of her. If anything, it's a genuinely healthy extrapolation of her dreams as Powder - to be useful, to help. If she's reaching the point where she thinks she really CAN make things instead of just breaking them, that's a legitimately good sign.
Vi is the obvious candidate to become the new Vander, and I think she will eventually. The first three episodes have taken her some of the way along a very complicated journey. A lot of people have pointed out that she sacrificed every part of her identity to try and help Caitlyn in her grief - she put on the uniform of the people who killed her parents and sold out Vander, the people who tortured her in prison. She compartmentalized her love for Powder and convinced herself she could kill her for Caitlyn, even though she demonstrably couldn't. She packed away everything except her moral code, and then Caitlyn nearly shot a child to get to Jinx, so Vi stopped her. And so she learns that Caitlyn didn't appreciate anything of what she was asking of her. She didn't understand the weight of the sacrifice Vi was making for her. She didn't see Vi as a partner, only as a tool for getting her shot at Jinx, and when Vi broke from that purpose, Caitlyn police brutality'd her and abandoned her at the bottom of a hole. We've never seen Vi at this kind of rock bottom before, because she always had her identity, her stubbornness, her anger. She gave them up for love, and when her guard was down, she was punished for it. Vi is the character most reluctant to change. She voices it overtly; she sees everyone else changing, she begs it to stop. Everyone is preserved in her memory from before the night everything went wrong. Powder's not Jinx now, Powder is dead and Jinx is a new problem. Ekko is still "Little Man." I think Vi can't start becoming whoever she's meant to be until she gets past that terror of change, and it looks like she can't do that until she loses absolutely everything.
I'm less clear on what to expect from Caitlyn, but I think it's going to be fascinating. She's really at her worst in this part of the show, and it's incredibly interesting. Her unchallenged worldview is on full display: the undercity is disgusting and evil, the enforcers are the pinnacle of goodness now that the one bad apple has been excised. She was doing Vi a favor giving her the badge, obviously; Vi deserves the badge so she'll kick up whatever fuss she needs to in order to make it happen. Vi's one of the good ones, so Vi can't be like the other Zaunites, those animals. Her mother sealed up The Gray to keep them from asphyxiating from the pollution? Well, they killed her mother, so they don't deserve to breathe that free air anymore. Vi defies her one time and Caitlyn snaps into the only alternative she can currently understand: you're just like them, you're my enemy, you're beneath me. She never really made an effort to understand Vi's world because she clearly thought she was saving her from it. You don't deserve to be down there in the dirt, you deserve to be up here where it's nice. The dichotomy of Piltover Good, Zaun Bad is so deeply ingrained in her that her raw grief has left it completely exposed. If Vi won't help her, she deserves to be left down there. I want to see where they go with this, because Caitlyn's at her own kind of rock bottom right now - a sniper's fixation on her target causing her to hurt and cast away every other priority. Ambessa's correctly identified her as a weapon and is precisely aiming her wherever she needs her to destroy, and Caitlyn is so fixated on Jinx she can't even tell. I expect "what are you shooting for?" to come back in a big way.
I don't know WHAT the hell is going on with Jayce and I am so excited to figure it out. They really sold the whole "whoops you've been meddling with forces far beyond your comprehension just like Heinmerdinger said" thing and the implications are fascinating.
In the same way that Jinx seems to be sort of building a role all her own instead of taking someone's place, Viktor seems to be doing the same thing. He's not taking anyone's place; what he's up to is totally new. He's doing exactly what he wanted to back in season one - using hextech to help the people in most desperate need. He can heal the poisoning of Shimmer and the toxins in Zaun. He has what nobody else in this show has - a form of power that is curative and presently unchallenged. It isn't a fight for him, not like everything else has been. All he's ever cared about was alleviating suffering, and as far as we can tell, now he can. Nobody else was doing anything to help. I am very intrigued to see where this goes and how the magic system gets fleshed out around him.
I have a hunch that wild magic situation might be yeeting Ekko out of the timeline for a bit. The act 2 preview had him on the Remembrance Wall, so I assume the firelights are gonna presume him dead for a minute - bit of a bummer, but if he comes back with his canonical time powers I'll take it.
Minor note, I liked how they highlighted that the council hall was aggressively non-wheelchair-accessible. A very elegant way to underline how Piltover has never actually been a beacon of progress and opportunity.
