NOTE: Season 3 spoilers ahead.
See also here, with a sample from an earlier part of the song.
I love APETITAN so much, I have to explain it here. The song has two distinct movements: one of chaos and madness, the other of strength and determination. Rather than a traditional piece where one movement leads into the other, though, APETITAN shifts back and forth between them, as if they're battling each other.
The chaotic movement is definitely the Beast Titan's theme, and it accompanies him well into season 4 of the anime. The determined movement has yet to play again following Erwin's death. It was definitely his theme.