Beginner Script Ladder

This ladder turns the first lessons into small complete scripts. Read the rungs in order. Each one adds one new scripting idea and is backed by a local script from ygopro-scripts.

The snippets use modern local s,id=GetID() style even when the source script uses the older c12345678 table style. The behavior pattern is the same.

Rung	Local source	New idea
1. Draw Spell	c55144522.lua	A basic activated effect with player target data.
2. Target and destroy	c5318639.lua	Official Chain targets and relation checks.
3. Destroy a current Group	c53129443.lua	Non-targeting Group action rebuilt at resolution.
4. Choose by highest stat	c97169186.lua	Min/max selection and tied Groups.
5. Continuous stat modifier	c10012614.lua	A card activation plus a separate face-up field effect.
6. Mandatory trigger	c11548522.lua	EVENT_* trigger flow and handler relation checks.
7. Quick-Play prompt	c14087893.lua	Hint timing and stronger target-state rechecks.
8. Trap response	c44095762.lua	Event-specific Trap activation and opponent-turn condition.

1. Draw Spell

Start with one activated Spell that draws 2 cards.

local s,id=GetID()

function s.initial_effect(c)
    local e1=Effect.CreateEffect(c)
    e1:SetCategory(CATEGORY_DRAW)
    e1:SetType(EFFECT_TYPE_ACTIVATE)
    e1:SetProperty(EFFECT_FLAG_PLAYER_TARGET)
    e1:SetCode(EVENT_FREE_CHAIN)
    e1:SetTarget(s.target)
    e1:SetOperation(s.activate)
    c:RegisterEffect(e1)
end

function s.target(e,tp,eg,ep,ev,re,r,rp,chk)
    if chk==0 then return Duel.IsPlayerCanDraw(tp,2) end
    Duel.SetTargetPlayer(tp)
    Duel.SetTargetParam(2)
    Duel.SetOperationInfo(0,CATEGORY_DRAW,nil,0,tp,2)
end

function s.activate(e,tp,eg,ep,ev,re,r,rp)
    local p,d=Duel.GetChainInfo(0,CHAININFO_TARGET_PLAYER,CHAININFO_TARGET_PARAM)
    Duel.Draw(p,d,REASON_EFFECT)
end

What this teaches:

Line	Purpose
SetType(EFFECT_TYPE_ACTIVATE)	This is a Spell/Trap Card activation.
chk==0	The activation is legal only if the draw can happen.
SetTargetPlayer and SetTargetParam	Store player data on the Chain Link.
GetChainInfo	Read that data back at resolution.

2. Target And Destroy

Next, target one Spell/Trap on the field and destroy it.

local s,id=GetID()

function s.initial_effect(c)
    local e1=Effect.CreateEffect(c)
    e1:SetCategory(CATEGORY_DESTROY)
    e1:SetType(EFFECT_TYPE_ACTIVATE)
    e1:SetCode(EVENT_FREE_CHAIN)
    e1:SetHintTiming(0,TIMING_END_PHASE+TIMING_EQUIP)
    e1:SetProperty(EFFECT_FLAG_CARD_TARGET)
    e1:SetTarget(s.target)
    e1:SetOperation(s.activate)
    c:RegisterEffect(e1)
end

function s.filter(c)
    return c:IsType(TYPE_SPELL+TYPE_TRAP)
end

function s.target(e,tp,eg,ep,ev,re,r,rp,chk,chkc)
    if chkc then
        return chkc:IsOnField() and s.filter(chkc) and chkc~=e:GetHandler()
    end
    if chk==0 then
        return Duel.IsExistingTarget(s.filter,tp,LOCATION_ONFIELD,LOCATION_ONFIELD,1,e:GetHandler())
    end
    Duel.Hint(HINT_SELECTMSG,tp,HINTMSG_DESTROY)
    local g=Duel.SelectTarget(tp,s.filter,tp,LOCATION_ONFIELD,LOCATION_ONFIELD,1,1,e:GetHandler())
    Duel.SetOperationInfo(0,CATEGORY_DESTROY,g,1,0,0)
end

function s.activate(e,tp,eg,ep,ev,re,r,rp)
    local tc=Duel.GetFirstTarget()
    if tc:IsRelateToEffect(e) then
        Duel.Destroy(tc,REASON_EFFECT)
    end
end

What this teaches:

Line	Purpose
EFFECT_FLAG_CARD_TARGET	The selected card becomes an official Chain target.
chkc	Manual target rechecks must match the filter.
Duel.SelectTarget	Records the target on the Chain Link.
IsRelateToEffect	The target may move before resolution.

3. Destroy A Current Group

Now remove targeting. This effect destroys all monsters currently on the field.

local s,id=GetID()

function s.initial_effect(c)
    local e1=Effect.CreateEffect(c)
    e1:SetCategory(CATEGORY_DESTROY)
    e1:SetType(EFFECT_TYPE_ACTIVATE)
    e1:SetCode(EVENT_FREE_CHAIN)
    e1:SetTarget(s.target)
    e1:SetOperation(s.activate)
    c:RegisterEffect(e1)
end

function s.target(e,tp,eg,ep,ev,re,r,rp,chk)
    if chk==0 then
        return Duel.IsExistingMatchingCard(aux.TRUE,tp,LOCATION_MZONE,LOCATION_MZONE,1,nil)
    end
    local g=Duel.GetMatchingGroup(aux.TRUE,tp,LOCATION_MZONE,LOCATION_MZONE,nil)
    Duel.SetOperationInfo(0,CATEGORY_DESTROY,g,#g,0,0)
end

function s.activate(e,tp,eg,ep,ev,re,r,rp)
    local g=Duel.GetMatchingGroup(aux.TRUE,tp,LOCATION_MZONE,LOCATION_MZONE,nil)
    Duel.Destroy(g,REASON_EFFECT)
end

What this teaches:

Line	Purpose
IsExistingMatchingCard	Legality checks that there is something to do.
GetMatchingGroup in target	Announces the current expected Group.
GetMatchingGroup in operation	Rebuilds the Group from the current field at resolution.

4. Choose By Highest Stat

This effect destroys the opponent's face-up monster with the highest DEF. If several tie, the player chooses one from the tied Group.

local s,id=GetID()

function s.initial_effect(c)
    local e1=Effect.CreateEffect(c)
    e1:SetCategory(CATEGORY_DESTROY)
    e1:SetType(EFFECT_TYPE_ACTIVATE)
    e1:SetCode(EVENT_FREE_CHAIN)
    e1:SetTarget(s.target)
    e1:SetOperation(s.activate)
    c:RegisterEffect(e1)
end

function s.filter(c)
    return c:IsFaceup() and c:IsDefenseAbove(0)
end

function s.target(e,tp,eg,ep,ev,re,r,rp,chk)
    if chk==0 then
        return Duel.IsExistingMatchingCard(s.filter,tp,0,LOCATION_MZONE,1,nil)
    end
    local g=Duel.GetMatchingGroup(s.filter,tp,0,LOCATION_MZONE,nil)
    local tg=g:GetMaxGroup(Card.GetDefense)
    Duel.SetOperationInfo(0,CATEGORY_DESTROY,tg,1,0,0)
end

function s.activate(e,tp,eg,ep,ev,re,r,rp)
    local g=Duel.GetMatchingGroup(s.filter,tp,0,LOCATION_MZONE,nil)
    if #g>0 then
        local tg=g:GetMaxGroup(Card.GetDefense)
        if #tg>1 then
            Duel.Hint(HINT_SELECTMSG,tp,HINTMSG_DESTROY)
            local sg=tg:Select(tp,1,1,nil)
            Duel.HintSelection(sg)
            Duel.Destroy(sg,REASON_EFFECT)
        else
            Duel.Destroy(tg,REASON_EFFECT)
        end
    end
end

What this teaches:

Line	Purpose
IsDefenseAbove(0)	Filters out candidates without usable DEF.
GetMaxGroup(Card.GetDefense)	Gets every card tied for highest DEF.
Group.Select	Chooses from the tied Group only when needed.

Read Min/Max Stat Card Selection after this rung.

5. Continuous Stat Modifier

A Continuous Spell often has one effect to activate the card and another effect for the rule it applies while face-up.

local s,id=GetID()

function s.initial_effect(c)
    local e1=Effect.CreateEffect(c)
    e1:SetType(EFFECT_TYPE_ACTIVATE)
    e1:SetCode(EVENT_FREE_CHAIN)
    c:RegisterEffect(e1)

    local e2=Effect.CreateEffect(c)
    e2:SetType(EFFECT_TYPE_FIELD)
    e2:SetRange(LOCATION_SZONE)
    e2:SetTargetRange(LOCATION_MZONE,0)
    e2:SetCode(EFFECT_UPDATE_ATTACK)
    e2:SetCondition(s.con)
    e2:SetValue(200)
    c:RegisterEffect(e2)
end

function s.con(e)
    local ph=Duel.GetCurrentPhase()
    local tp=Duel.GetTurnPlayer()
    return tp==e:GetHandlerPlayer() and ph>=PHASE_BATTLE_START and ph<=PHASE_BATTLE
end

What this teaches:

Line	Purpose
First effect	Activates the card.
Second effect	Applies the continuous ATK update.
SetRange(LOCATION_SZONE)	The modifier exists while this card is face-up in the Spell & Trap Zone.
SetTargetRange(LOCATION_MZONE,0)	The modifier applies to the controller's monsters.

6. Mandatory Trigger

This trigger activates when the handler is sent to the GY and returns the handler to the Deck.

local s,id=GetID()

function s.initial_effect(c)
    local e1=Effect.CreateEffect(c)
    e1:SetDescription(aux.Stringid(id,0))
    e1:SetCategory(CATEGORY_TODECK)
    e1:SetType(EFFECT_TYPE_SINGLE+EFFECT_TYPE_TRIGGER_F)
    e1:SetCode(EVENT_TO_GRAVE)
    e1:SetTarget(s.tdtg)
    e1:SetOperation(s.tdop)
    c:RegisterEffect(e1)
end

function s.tdtg(e,tp,eg,ep,ev,re,r,rp,chk)
    if chk==0 then return true end
    Duel.SetOperationInfo(0,CATEGORY_TODECK,e:GetHandler(),1,0,0)
end

function s.tdop(e,tp,eg,ep,ev,re,r,rp)
    local c=e:GetHandler()
    if c:IsRelateToEffect(e) then
        Duel.SendtoDeck(c,nil,SEQ_DECKSHUFFLE,REASON_EFFECT)
    end
end

What this teaches:

Line	Purpose
EFFECT_TYPE_SINGLE+EFFECT_TYPE_TRIGGER_F	The handler has a mandatory trigger.
EVENT_TO_GRAVE	The event watched by the trigger.
e:GetHandler()	The card whose script owns the effect.
IsRelateToEffect	The handler must still be related to its resolving trigger.

7. Quick-Play Prompt And Recheck

Quick-Play Spells still use EFFECT_TYPE_ACTIVATE. The card type and core speed handling make the activation fast; the script gives the client better prompt timing and rechecks the target state at resolution.

local s,id=GetID()

function s.initial_effect(c)
    local e1=Effect.CreateEffect(c)
    e1:SetCategory(CATEGORY_POSITION+CATEGORY_MSET)
    e1:SetType(EFFECT_TYPE_ACTIVATE)
    e1:SetProperty(EFFECT_FLAG_CARD_TARGET)
    e1:SetCode(EVENT_FREE_CHAIN)
    e1:SetHintTiming(TIMING_BATTLE_PHASE,TIMINGS_CHECK_MONSTER+TIMING_BATTLE_PHASE)
    e1:SetTarget(s.target)
    e1:SetOperation(s.activate)
    c:RegisterEffect(e1)
end

function s.filter(c)
    return c:IsFaceup() and c:IsCanTurnSet()
end

function s.target(e,tp,eg,ep,ev,re,r,rp,chk,chkc)
    if chkc then return chkc:IsLocation(LOCATION_MZONE) and s.filter(chkc) end
    if chk==0 then
        return Duel.IsExistingTarget(s.filter,tp,LOCATION_MZONE,LOCATION_MZONE,1,nil)
    end
    Duel.Hint(HINT_SELECTMSG,tp,HINTMSG_FACEUP)
    local g=Duel.SelectTarget(tp,s.filter,tp,LOCATION_MZONE,LOCATION_MZONE,1,1,nil)
    Duel.SetOperationInfo(0,CATEGORY_POSITION,g,1,0,0)
end

function s.activate(e,tp,eg,ep,ev,re,r,rp)
    local tc=Duel.GetFirstTarget()
    if tc:IsRelateToEffect(e) and tc:IsLocation(LOCATION_MZONE) and tc:IsFaceup() then
        Duel.ChangePosition(tc,POS_FACEDOWN_DEFENSE)
    end
end

What this teaches:

Line	Purpose
SetHintTiming	Tells the client when prompts are useful.
IsCanTurnSet	The target must be able to perform the action.
Resolution rechecks	The target must still be related, in the right location, and face-up.

8. Trap Response

This Trap responds to an attack announcement and destroys the opponent's Attack Position monsters.

local s,id=GetID()

function s.initial_effect(c)
    local e1=Effect.CreateEffect(c)
    e1:SetCategory(CATEGORY_DESTROY)
    e1:SetType(EFFECT_TYPE_ACTIVATE)
    e1:SetCode(EVENT_ATTACK_ANNOUNCE)
    e1:SetCondition(s.condition)
    e1:SetTarget(s.target)
    e1:SetOperation(s.activate)
    c:RegisterEffect(e1)
end

function s.condition(e,tp,eg,ep,ev,re,r,rp)
    return tp~=Duel.GetTurnPlayer()
end

function s.filter(c)
    return c:IsAttackPos()
end

function s.target(e,tp,eg,ep,ev,re,r,rp,chk)
    if chk==0 then
        return Duel.IsExistingMatchingCard(s.filter,tp,0,LOCATION_MZONE,1,nil)
    end
    local g=Duel.GetMatchingGroup(s.filter,tp,0,LOCATION_MZONE,nil)
    Duel.SetOperationInfo(0,CATEGORY_DESTROY,g,#g,0,0)
end

function s.activate(e,tp,eg,ep,ev,re,r,rp)
    local g=Duel.GetMatchingGroup(s.filter,tp,0,LOCATION_MZONE,nil)
    if #g>0 then
        Duel.Destroy(g,REASON_EFFECT)
    end
end

What this teaches:

Line	Purpose
EVENT_ATTACK_ANNOUNCE	The Trap is not free-chain; it responds to a specific event.
tp~=Duel.GetTurnPlayer()	The local script only lets the defending player activate it.
Rebuilt Group	The operation destroys the current matching monsters at resolution.

Practice Exercises

Do these after reading the rungs. The goal is not to invent a complicated card; it is to change one moving part at a time and keep the activation flow correct.

Exercise	Start from	Change
Draw 1 instead of 2.	Rung 1	Change the draw amount in chk==0, SetTargetParam, SetOperationInfo, and resolution.
Destroy only face-up Spells/Traps.	Rung 2	Add c:IsFaceup() to the target filter and keep the chkc branch consistent.
Destroy all opponent monsters only.	Rung 3	Change the matching locations to your opponent's Monster Zone.
Lowest ATK instead of highest DEF.	Rung 4	Use Card.GetAttack, GetMinGroup, and an ATK-valid filter.
Continuous DEF boost.	Rung 5	Change EFFECT_UPDATE_ATTACK to EFFECT_UPDATE_DEFENSE.
Optional trigger.	Rung 6	Change the type to EFFECT_TYPE_SINGLE+EFFECT_TYPE_TRIGGER_O and add a useful description.
Different Quick-Play target.	Rung 7	Replace the position filter with a Spell/Trap target filter from Rung 2.
Trap that responds to a Summon.	Rung 8	Compare with local c4206964.lua and use a summon-success event.

Check each exercise with the same rhythm:

1. Does chk==0 prove that the required action can happen?
2. If the effect targets, does the chkc branch match the target selection?
3. Does Duel.SetOperationInfo announce the action honestly?
4. Does the operation rebuild or recheck the current game state before acting?
5. Are prompts and hints visible enough for the client?

Move Forward

After the ladder, the main pieces are in your hands:

If you want to script...	Read next
Better activation checks	Activation Legality
More target patterns	Targeting Flow
Resolution choices and stored Groups	Selection And Group Handling
Client prompts	Client UI And Prompt Behavior
Continuous rules	Effects That Apply Continuously
Spell/Trap variants	Spell Card Patterns and Trap Card Patterns
Debugging mistakes	Common Script Errors And Debugging
Your first original script	Write Your First Custom Card

Useful API pages:

• Effect.CreateEffect
• Effect.SetType
• Effect.SetCode
• Effect.SetTarget
• Effect.SetOperation
• Duel.SetOperationInfo
• Duel.SelectTarget
• Duel.SelectMatchingCard
• Duel.GetMatchingGroup
• Card.IsRelateToEffect
• Group.GetMaxGroup