(SPOILERS!!! - DON'T WATCH IF YOU HAVEN'T SEEN THE SHOW)
The beginning and the ending of "Over the Garden Wall" put together, forming the main song of the series - "Into the Unknown"

Lyrics:

Led through the mist
By the milk light of moon
All that was lost is revealed

Our long bygone burdens
Mere echoes of the spring
But where have we come?

And where shall we end?
If dreams can't come true
Than why not pretend?

How the gentle wind
Beckons through the leaves
As autumn colors fall

Dancing in a swirl
Of golden memories
The loveliest lies of all

The loveliest... lies... of all...