Generate a YGOPro Lua script for the following Yu-Gi-Oh card effect:
During your Main Phase, you can Normal Summon 1 Level 4 or lower Sea Serpent-Type monster in addition to your Normal Summon/Set. (You can only gain this effect once per turn.) When this card is sent to the Graveyard to activate a WATER monster's effect: Target 1 face-up card your opponent controls; destroy that target.
--海皇の重装兵
--Atlantean Heavy Infantry
local s,id=GetID()
function s.initial_effect(c)
	--Extra Normal Summon
	local e1=Effect.CreateEffect(c)
	e1:SetDescription(aux.Stringid(id,1))
	e1:SetType(EFFECT_TYPE_FIELD)
	e1:SetRange(LOCATION_MZONE)
	e1:SetTargetRange(LOCATION_HAND|LOCATION_MZONE,0)
	e1:SetCode(EFFECT_EXTRA_SUMMON_COUNT)
	e1:SetTarget(s.extg)
	c:RegisterEffect(e1)
	--Destroy 1 card
	local e2=Effect.CreateEffect(c)
	e2:SetDescription(aux.Stringid(id,0))
	e2:SetCategory(CATEGORY_DESTROY)
	e2:SetType(EFFECT_TYPE_SINGLE+EFFECT_TYPE_TRIGGER_F)
	e2:SetProperty(EFFECT_FLAG_CARD_TARGET)
	e2:SetCode(EVENT_TO_GRAVE)
	e2:SetCondition(s.descon)
	e2:SetTarget(s.destg)
	e2:SetOperation(s.desop)
	c:RegisterEffect(e2)
end
function s.extg(e,c)
	return c:IsLevelBelow(4) and c:IsRace(RACE_SEASERPENT)
end
function s.descon(e,tp,eg,ep,ev,re,r,rp)
	return e:GetHandler():IsReason(REASON_COST) and re:IsActivated() and re:IsMonsterEffect()
		and re:GetHandler():IsAttribute(ATTRIBUTE_WATER)
end
function s.destg(e,tp,eg,ep,ev,re,r,rp,chk,chkc)
	if chkc then return chkc:IsOnField() and chkc:IsControler(1-tp) and chkc:IsFaceup() end
	if chk==0 then return true end
	Duel.Hint(HINT_SELECTMSG,tp,HINTMSG_DESTROY)
	local g=Duel.SelectTarget(tp,Card.IsFaceup,tp,0,LOCATION_ONFIELD,1,1,nil)
	Duel.SetOperationInfo(0,CATEGORY_DESTROY,g,#g,0,0)
end
function s.desop(e,tp,eg,ep,ev,re,r,rp)
	local tc=Duel.GetFirstTarget()
	if tc and tc:IsRelateToEffect(e) and tc:IsFaceup() then
		Duel.Destroy(tc,REASON_EFFECT)
	end
end