Bump this up.
The White Walkers, assuming we are talking about the actual White Walkers and not the Wrights.
They are faster than the Mannequins and have a higher level of intelligence, not to mention actual fighting skill and the fact that Mannequins dont have the destructive power to get rid of them or Dragonglass (Obsidian for anyone who watches the show)/Fire/Dragonsteel (Valyrian Steel for anyone who watches the show, I also can't remember if this has actually worked on them but I do remember Sam saying that Dragonsteel can kill them. Been awhile since I read the books so my knowledge is sketchy on the finer details) to exploit their only known weaknesses.
Might require chopping them into pieces but the White Walkers should finish this up without too much trouble.