[Kurona]

Really liked the explanation for the sillier, stranger bottles -- they're literally just Soichi making stupid stuff up to throw off Evolt, lol. Still leaves Santa as the slightest little enigma, mind.

Sento's dad being the final villain would, I think, bring a lot of the series' themes and his character arc full circle -- a lot of it has been about not only moving on from destructive, toxic elements of your past but also using them to build a better future. Sento's last two powerups have been great examples of this -- the Hazard Trigger was used for Rabbitrabbit/Tanktank, while his past self was used for Genius.
With how much Sento's dad has been prevalent throughout the series and his being an ally of Evolt, I can easily see the next few episodes portraying him as a shadowy third party (or, well; sixth or seventh by this point giving Build's power plays) who's been manipulating things from behind the scenes. We'll see.