While Silco, Ambessa, and Piltover's war council were villains throughout Arcane, the finale of season 2 confirms our suspicion of who the real big bad is that might show up in future League of Legends TV shows.
If you've not finished Arcane, turn back now, as there are spoilers ahead for seasons 1 and 2.
As Andy spotted, there has been a crow theme throughout Arcane. Crows frequently watch our main characters and the events in the series very carefully. Jinx blasts one while she revisits the arcade where she spent her childhood, and they flock around the building where she kills Silco.
As well as the physical presence of the birds, Jinx gets a lot of crow-like visuals. When she lets go of Powder, her throne has black feathers on it, and during her battle with Ekko she's represented as a crow.
As noted by Dexerto, one small moment in the season 2 finale really ties the whole crow motif together. When a crow at the end opens its eyes and reveals a demonic row of three of them along its head, it's clear that Swain, the Grand General of Noxus, has been keeping an eye on things.
Swain is the ruler of Noxus, where Ambessa is from. So, he's already likely had a hand in the events of the show. This reveal makes him a Thanos-like enemy – it's like the post credits scene of Avengers Assemble where we see the mad titan say "fine, I'll do it myself."
If you've just finished Arcane and still have some questions, check out our guide on the Arcane season 2 ending explained.