[CFrame] Moving the characters head to your mouse.Hit??

EDIT: I realized I was completely wrong. Use mouse.Hit.Z

mouse.Hit returns a CFrame value.

local plr = game.Players.LocalPlayer
local m = plr:GetMouse()

m.Button1Down:connect(function(mouse)
	print(m.Hit)
end)

-> 0.0844552889, 0, -0.412481308, -0.999974728, 0.00373247126, -0.0060590161, -0, 0.851417065, 0.524489343, 0.00711639086, 0.524476111, -0.851395488

I think what you're looking for is mouse.Hit.p which returns the position of a part

local plr = game.Players.LocalPlayer
local m = plr:GetMouse()

m.Button1Down:connect(function(mouse)
	print(m.Hit.p.Z)
end)

-> 0,0,0

Use mouse.Hit.p.Z to get the Z value, so your new code would be:

local plr=game.Players.LocalPlayer
local mouse=plr:GetMouse()

plr.Character.Torso.Neck.C0=CFrame.new(0,1.5,0)*CFrame.Angles(0,0,mouse.Hit.p.Z)