Here's a Finnish Christmas song that starts as relatively mellow but morphs into something like metal or hard rock at around 2 minutes (this is part of an event that presents Christmas songs in "heavier" style after all). I'll add my own translation of the lyrics below.
Night falls on the Christmas eve
Veil of darkness covers a cold land
A lonely figure makes his way
In the frost with a candle in hand
Just a small boy, face lacking in joy
Through darkness with no life in sight
Coldness' bite he will brave, and his mother's grave
He now mournfully blesses with light
A flame so softly shimmering
Lightens the grave of his mother dearest
His waitful eyes fill with longing
For the birth of new hope and calm rest
Can Christmas still bring a sense of good will
For his family in their hollowed place
Dark quiet adorns the home that still mourns
As if missing its blessing and grace
A voice so calming and soft
This precious small boy now hears
Giving warm words of comfort
Calming his troubles and fears
Do not let worries win, but raise your chin
Every moment with you I will stay
Through life's trials, as the first Christmas' Child
I'm the light that will guide your way
The very first Christmas did I stay
In a stable with oxen and hay
Where the stars gave their twinkling light
And from distant lands wise men arrived
As your sorrow will wane, with you I'll remain
Making Christmases joyful and bright
And soon you will see how night's shadows will flee
When graced with the brightest light