Why does he suddenly say "breathe it in"? What does "it" refer here?
Maui has made up a narcissistic song about himself. When he says, "yes, it's really me, Maui, breathe it in", "breathe it in" is meant in a similar way to "let it sink in.", which means to 'understand or accept'. "It" doesn't really refer to anything here, the main purpose of this phrase is to exaggerate Maui's greatness and make Moana feel amazement at being in his presence. Unlike in this video, when "breathe it in" is used in the conventional sense, it is used to tell someone to breathe in the air or smells around them. Ex: I love the smell of freshly baked cookies. Breathe it in! Ex: The air is so fresh by the ocean. Breathe in that air!