mir, den or meinen?

[Fred]

Hello,

This is the first line from this book: https://www.amazon.co.uk/Ich-bin-viele-Bobiverse-German-ebook/dp/B077C267FB/ref=sr_1_2?keywords=ich+bin+viele&qid=1572024404&sr=8-2

»Sie werden mir also den Kopf abschneiden.«, meaning “So You’ll cut my head off.”

Can anyone tell me why it has both 'mir' and 'den' in it?

Couldn't you just use one or the other?

Also, could you say "Sie werden also meinen Kopf abschneiden" instead?

Thanks for any help.

Fred.