The Night King vs Legolas

An eldritch ice demon with a javelin

An elf with a bow

RULES

Bloodlusted, Morals off

Win by any means

Random encounter, therefore no prior knowledge

Presumably Legolas can't kill him without dragon glass (which is questionable since he was created with it), Valyrian steel, or a dragon's breath. So Night King by default.

Night King

A night elf is born

Night King.

Night King.

Legolas wins.

NK unless Legolas has Dragon glass or Valyrian tip arrows.

The Night king is pretty broken for anyone outside his universe. As it stands right now, only dragonglass and valyrian steel can put him down, and even those are only in theory considering he's the OG Whitewalker. Legolas has no way to put him down without those weapons.