The only being capable of defeating Chansilla, is Kirby
Think about it. The two of them are pink and round, highly adorable-looking creatures of eldritch nature and reality-breaking powers, with Chansilla being a literal MissingNo Ultra Being (and is thus, strong enough to destroy the entire timeline, aka the save file), and Kirby being a reincarnation of Void (which makes him as much of an Eldritch Abomination as the likes of Void Termina) while also being strong enough to defeat the original Void. However, while Chansilla is a sadistic psychopatic Ax-Crazy monster that threatens the life of everything and is implied to have been around for a long time, Kirby is a benevolent, extremely friendly Nice Guy who protects the universe and who's merely a young boy. It would make sense for Kirby to be the one who can defeat Chansilla, after all, he has a lot of experience destroying Eldritch Abominations, right? Eric's nightmare of his mother in-law screaming at him for all the politically incorrect jokes he's made with Rangu was a prophetic dream
It was the result of him spending too much time with Rangu, he absorbed some of Rangu's clairvoyant vibes by being close to him and ended up absorbing enough of them to be capable of predicting future events through dreaming.