em npc crie um arquivo Rulfs.xml:

<?xml version="1.0" encoding="UTF-8"?>
<npc name="Rulfs" script="Rulfs.lua" walkinterval="2000" floorchange="0">
	<health now="100" max="100"/>
	<look type="128" head="17" body="54" legs="114" feet="0" addons="2"/>
</npc>

em npc/scripts crie um arquivo Rulfs.lua

local keywordHandler = KeywordHandler:new()
local npcHandler = NpcHandler:new(keywordHandler)
NpcSystem.parseParameters(npcHandler)
local talkState = {}

function onCreatureAppear(cid)				npcHandler:onCreatureAppear(cid) 			end
function onCreatureDisappear(cid) 			npcHandler:onCreatureDisappear(cid) 		end
function onCreatureSay(cid, type, msg) 		npcHandler:onCreatureSay(cid, type, msg) 	end
function onThink() 							npcHandler:onThink() 						end
function onPlayerEndTrade(cid)				npcHandler:onPlayerEndTrade(cid)			end
function onPlayerCloseChannel(cid)			npcHandler:onPlayerCloseChannel(cid)		end



local nome = "Rulfs" -- nome do monstro que vai parecer


local function greetCallback(cid)
	local msg = 'Olá '.. getCreatureName(cid) ..", vem me desafiar a um duelo?"
	npcHandler:say(msg,cid)
    npcHandler:addFocus(cid)
	return false
end
function creatureSayCallback(cid, type, msg)
	if string.lower(msg) == 'bye' or string.lower(msg) == 'xau' then
		npcHandler:resetNpc(cid)
		return false
	end
    if(not npcHandler:isFocused(cid)) then 
        return false
    end
	if (msgcontains(msg, 'sim') or msgcontains(msg, 'yes')) then
		local pos = getCreaturePosition(getNpcId())
		selfSay('Então venha.',cid)
		doCreatureSay(getNpcId(), "MuHuashAUhashSHUuSA", TALKTYPE_MONSTER_YELL)
		npcHandler:resetNpc(cid)
		doRemoveCreature(getNpcId())
		doCreateMonster(nome, pos)
	end
	if (msgcontains(msg, 'nao') or msgcontains(msg, 'no') or msgcontains(msg, 'não')) then
		selfSay('Então tchau.', cid)
		npcHandler:resetNpc(cid)
		return false
	end
		
	return true
end

npcHandler:setCallback(CALLBACK_GREET, greetCallback)
npcHandler:setCallback(CALLBACK_MESSAGE_DEFAULT, creatureSayCallback)
npcHandler:addModule(FocusModule:new()) 

crie um arquivo em na pasta monster com o nome Rulfs.xml:

<?xml version="1.0" encoding="UTF-8"?>
<monster name="Rulfs" nameDescription="a rulfs" race="blood" experience="900" speed="220" manacost="0">
	<health now="1000" max="1000"/>
	<look type="128" head="17" body="54" legs="114" feet="0" addons="2" corpse="6080"/>
	<targetchange interval="5000" chance="8"/>
	<strategy attack="100" defense="0"/>
	<flags>
		<flag summonable="0"/>
		<flag attackable="1"/>
		<flag hostile="1"/>
		<flag illusionable="0"/>
		<flag convinceable="0"/>
		<flag pushable="0"/>
		<flag canpushitems="1"/>
		<flag canpushcreatures="1"/>
		<flag targetdistance="1"/>
		<flag staticattack="90"/>
		<flag runonhealth="500"/>
	</flags>
	<attacks>
		<attack name="melee" interval="2000" skill="30" attack="50" poison="150"/>
		<attack name="speed" interval="1000" chance="10" range="7" speedchange="-600" duration="20000">
			<attribute key="areaEffect" value="redshimmer"/>
		</attack>
		<attack name="lifedrain" interval="1000" chance="40" radius="4" target="0" min="-120" max="-250">
			<attribute key="areaEffect" value="rednote"/>
		</attack>
	</attacks>
	<defenses armor="15" defense="20">
		<defense name="healing" interval="1000" chance="25" min="113" max="187">
			<attribute key="areaEffect" value="blueshimmer"/>
		</defense>
	</defenses>
	<elements>
		<element firePercent="100"/>
		<element deathPercent="100"/>
		<element earthPercent="100"/>
		<element holyPercent="-20"/>
	</elements>
	<immunities>
		<immunity lifedrain="1"/>
		<immunity paralyze="1"/>
		<immunity invisible="1"/>
	</immunities>
	<voices interval="5000" chance="10">
		<voice sentence="HAHAHAHAHA"/>

	</voices>
	<loot>
		<item id="2148" countmax="60" chance="11250"/><!-- gold coin -->
		<item id="2148" countmax="40" chance="11250"/><!-- gold coin -->
		<item id="2144" chance="2000"/><!-- black pearl -->
		<item id="2656" chance="650"/><!-- blue robe -->
		<item id="2047" chance="70000"/><!-- candle stick -->
		<item id="2237" chance="19000"/><!-- dirty cape -->
		<item id="2177" chance="50"/><!-- life crystal -->
		<item id="2071" chance="1333"/><!-- lyre -->
		<item id="2560" chance="7250"/><!-- mirror -->
		<item id="2411" chance="1600"/><!-- poison dagger -->
		<item id="2655" chance="800"/><!-- red robe -->
		<item id="2214" chance="860"/><!-- ring of healing -->
		<item id="2170" chance="8300"/><!-- silver amulet -->
		<item id="2134" chance="1750"/><!-- silver brooch -->
		<item id="2657" chance="60000"/><!-- simple dress -->
		<item id="2197" chance="1100"/><!-- stone skin amulet -->
		<item id="7589" chance="650"/><!-- strong mana potion -->
		<item id="2175" chance="900"/><!-- spellbook -->
		<item id="2143" chance="410"/><!-- white pearl -->
		<item id="7884" chance="240"/><!-- terra mantle -->
		<item id="2121" chance="410"/><!-- wedding ring -->
		<item id="2124" chance="100"/><!-- crystal ring -->
	</loot>
</monster>

e em monster.xml coloque isso:

	<monster name="Rulfs" file="Rulfs.xml"/>

depois em creaturescript/scripts crie um arquivo Rulfs.lua com isso:

local monstro = "Rulfs" -- nome do monstro
local NPC = "Rulfs" -- nome do NPC
function onKill(cid, target, damage, flags)
	if getCreatureName(target) == monstro then
		doCreateNpc(NPC, getCreaturePosition(target))
	end
	if getCreatureName(cid) == monstro then
		local pos = getCreaturePosition(cid)
		doRemoveCreature(cid)
		doCreateNpc(NPC, pos)
	end
	return true
end

depois em login.lua cole isso antes do return true:

	registerCreatureEvent(cid, "desafio")

e em creaturescript.xml coloque isso:

<event type="kill" name="desafio" event="script" value="Rulfs.lua"/>

qualquer erro retorne