No game in history uses leitmotifs
better than Undertale.
It runs the same few themes through nearly every song in the game. Toby Fox not only weaves motifs through varying genre, style, mood, and context, he also (and this blew my mind) significantly slows down some of them to the point where they're not even overtly distinguishable as a motif. You don't even recognize you're listening to a familiar theme at 12% the original tempo, only that this seemingly new song feels emotionally significant in ways you can't quite put your finger on.
The themes of Undertale plant their roots in your subconscious from the moment you boot up the game. You might not recognize what you're listening to is a motif until hours later when you've heard it in half a dozen other contexts. Every new song that borrows a theme is made more powerful by its every preceding instance. So by the last third of the game, even the new songs feel
lived in. Powerful. Evocative.
This is especially effective in a game with as singular a thesis as Undertale. Every element of that game is reinforcing the idea that
nothing is disposable. Every memory, every experience, every action, every choice, every life. Nothing is without impact. Ours on others, others on us.
The motifs weave their way through the score like veins in a shared body, carrying, like blood, the weight of their history and context to every new piece.
I genuinely believe Toby Fox's composition is genius. Powerful, varied, and unrivaled in its use of motif. The synergy of the score with the themes and intent of the game demonstrates a harmony only truly inspired auteur projects like this could ever hope to accomplish.
EDIT:
tl;dr:
Undertale wouldn't be half the game it is without its leitmotifs. They're that important.
Basically all there is to it.
