Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
Once per turn, by paying 300 Life Points, rearrange the face-down Defense Position monsters in your Main Monster Zones, then return them in face-down Defense Position.
--うごめく影
--Shifting Shadows
local s,id=GetID()
function s.initial_effect(c)
	--Activate
	local e1=Effect.CreateEffect(c)
	e1:SetType(EFFECT_TYPE_ACTIVATE)
	e1:SetCode(EVENT_FREE_CHAIN)
	c:RegisterEffect(e1)
	--Shuffle your face-down monsters
	local e2=Effect.CreateEffect(c)
	e2:SetDescription(aux.Stringid(id,0))
	e2:SetType(EFFECT_TYPE_IGNITION)
	e2:SetRange(LOCATION_SZONE)
	e2:SetCountLimit(1)
	e2:SetCost(Cost.PayLP(300))
	e2:SetTarget(s.target)
	e2:SetOperation(s.operation)
	c:RegisterEffect(e2)
end
function s.target(e,tp,eg,ep,ev,re,r,rp,chk)
	if chk==0 then return Duel.IsExistingMatchingCard(Card.IsFacedown,tp,LOCATION_MMZONE,0,2,nil) end
end
function s.operation(e,tp,eg,ep,ev,re,r,rp)
	local g=Duel.GetMatchingGroup(Card.IsFacedown,tp,LOCATION_MMZONE,0,nil)
	Duel.ShuffleSetCard(g)
end