Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
All monsters are changed to Attack Position, also their battle positions cannot be changed. (Flip Effects are not activated.) Once per turn: You can reveal any number of Fiend monsters in your hand; this card gains 300 ATK for each, until the end of this turn.
--軍神ガープ
--Gaap the Divine Soldier
local s,id=GetID()
function s.initial_effect(c)
	--Pos Change
	local e1=Effect.CreateEffect(c)
	e1:SetType(EFFECT_TYPE_FIELD)
	e1:SetCode(EFFECT_SET_POSITION)
	e1:SetProperty(EFFECT_FLAG_SET_AVAILABLE)
	e1:SetRange(LOCATION_MZONE)
	e1:SetTargetRange(LOCATION_MZONE,LOCATION_MZONE)
	e1:SetValue(POS_FACEUP_ATTACK+NO_FLIP_EFFECT)
	c:RegisterEffect(e1)
	local e2=e1:Clone()
	e2:SetCode(EFFECT_CANNOT_CHANGE_POSITION)
	c:RegisterEffect(e2)
	--atkup
	local e3=Effect.CreateEffect(c)
	e3:SetDescription(aux.Stringid(id,0))
	e3:SetCategory(CATEGORY_ATKCHANGE)
	e3:SetType(EFFECT_TYPE_IGNITION)
	e3:SetCountLimit(1)
	e3:SetRange(LOCATION_MZONE)
	e3:SetCost(s.atcost)
	e3:SetOperation(s.atop)
	c:RegisterEffect(e3)
end
function s.cfilter(c)
	return c:IsRace(RACE_FIEND) and not c:IsPublic()
end
function s.atcost(e,tp,eg,ep,ev,re,r,rp,chk)
	if chk==0 then return Duel.IsExistingMatchingCard(s.cfilter,tp,LOCATION_HAND,0,1,nil) end
	Duel.Hint(HINT_SELECTMSG,tp,HINTMSG_CONFIRM)
	local g=Duel.SelectMatchingCard(tp,s.cfilter,tp,LOCATION_HAND,0,1,63,nil)
	Duel.ConfirmCards(1-tp,g)
	Duel.ShuffleHand(tp)
	e:SetLabel(#g)
end
function s.atop(e,tp,eg,ep,ev,re,r,rp)
	local c=e:GetHandler()
	if c:IsFacedown() or not c:IsRelateToEffect(e) then return end
	local e1=Effect.CreateEffect(c)
	e1:SetType(EFFECT_TYPE_SINGLE)
	e1:SetCode(EFFECT_UPDATE_ATTACK)
	e1:SetProperty(EFFECT_FLAG_CANNOT_DISABLE)
	e1:SetValue(e:GetLabel()*300)
	e1:SetReset(RESETS_STANDARD_PHASE_END)
	c:RegisterEffect(e1)
end