Why did they decide to kill off Nick? anyone know?

"We just felt that to really make the stakes of what these guys are dealing with feel real, to really ground it in an emotional reality, they just couldn't be walking around doing magic like it was no big deal. Unfortunately, there was just no better way to explore this idea of action and consequences than one of their own dying."
—Andrew Miller, EP

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Down tells Charles to kill Nick, to kill the demon that was inside.

I don't know. It made me so angry! He was one of my favourite's from the books, & they already cut most of the main characters.. grr..

The demon was inside him. And the only way to kill demons is to drown them または burn the. So they drowned nixk to drown the demon

They tought he was dangerous so they killed him