Pendulum Procedure Guide

Pendulum scripts are two cards in one file: a monster script plus the behavior the same card has while it is in a Pendulum Zone. The normal starting point is aux.EnablePendulumAttribute. It registers the shared Pendulum Summon procedure and, by default, the simple activation effect that lets the player activate the Pendulum Monster from the hand as a Spell.

Most of your script work then falls into one of three lanes: Pendulum Zone effects, monster effects, and effects that place or move Pendulum Cards.

The Three Jobs

Job	Where it usually lives	What it does
Pendulum Summon procedure	Each Pendulum Monster script	Registers an EFFECT_SPSUMMON_PROC_G from LOCATION_PZONE with SUMMON_TYPE_PENDULUM.
Pendulum Zone effects	The same card script, usually after the helper call	Uses SetRange(LOCATION_PZONE) for effects that apply while the card is in a Pendulum Zone.
Placement and special cases	Monster effects, Spell/Trap effects, or Special Summon Monster scripts	Moves cards to a Pendulum Zone, checks scales, grants extra Pendulum Summons, or completes revive-limit procedure handling.

For an ordinary Pendulum Monster, start with the procedure helper. Then add the Pendulum Zone effects and monster effects as separate Effect.CreateEffect blocks.

Standard Pendulum Pattern

Junoldo the Shadespirit Power Patron (c10266279.lua) shows the regular shape:

function s.initial_effect(c)
    aux.EnablePendulumAttribute(c)

    local e1=Effect.CreateEffect(c)
    e1:SetDescription(aux.Stringid(id,0))
    e1:SetCategory(CATEGORY_DRAW+CATEGORY_HANDES_SELF+CATEGORY_DESTROY)
    e1:SetType(EFFECT_TYPE_FIELD+EFFECT_TYPE_TRIGGER_O)
    e1:SetProperty(EFFECT_FLAG_DELAY)
    e1:SetCode(EVENT_SPSUMMON_SUCCESS)
    e1:SetRange(LOCATION_PZONE)
    e1:SetCountLimit(1,id)
    e1:SetCondition(s.drcon)
    e1:SetTarget(s.drtg)
    e1:SetOperation(s.drop)
    c:RegisterEffect(e1)
end

Read that as:

Piece	Meaning
aux.EnablePendulumAttribute(c)	Makes the card usable as a Pendulum Card and gives it the shared Pendulum Summon procedure.
SetRange(LOCATION_PZONE)	Makes the effect apply only while the card is in a Pendulum Zone.
EFFECT_TYPE_FIELD+EFFECT_TYPE_TRIGGER_O	Watches a game event from the Pendulum Zone and may activate when its condition is met.

Pendulum Zone effects are not all the same type. They can be continuous field effects, optional triggers, Ignition Effects, Quick Effects, or activation effects, depending on the card text. The shared detail is the range: LOCATION_PZONE.

What EnablePendulumAttribute Builds

Local procedure.lua creates the Pendulum Summon procedure like this:

local e1=Effect.CreateEffect(c)
e1:SetDescription(1163)
e1:SetType(EFFECT_TYPE_FIELD)
e1:SetCode(EFFECT_SPSUMMON_PROC_G)
e1:SetProperty(EFFECT_FLAG_CANNOT_DISABLE+EFFECT_FLAG_UNCOPYABLE)
e1:SetRange(LOCATION_PZONE)
e1:SetCondition(Auxiliary.PendCondition)
e1:SetOperation(Auxiliary.PendOperation)
e1:SetValue(SUMMON_TYPE_PENDULUM)
c:RegisterEffect(e1)

This is a rule procedure, not an activated effect. It does not create a Chain Link. The core asks the condition whether a Pendulum Summon is available, then the operation lets the player choose the monsters to Summon.

The same helper also registers a global Draw Phase Start reset the first time a Pendulum procedure is enabled:

Auxiliary.PendulumChecklist=0

That checklist is how the shared helper remembers whether each player has used their regular Pendulum Summon for the turn.

By default, the helper also registers the simple "activate this Pendulum Card from the hand" effect:

local e2=Effect.CreateEffect(c)
e2:SetDescription(1160)
e2:SetType(EFFECT_TYPE_ACTIVATE)
e2:SetCode(EVENT_FREE_CHAIN)
e2:SetRange(LOCATION_HAND)
c:RegisterEffect(e2)

Pass false as the second argument when the card should not receive that default hand activation effect:

aux.EnablePendulumAttribute(c,false)

Supreme King Z-ARC (c13331639.lua) uses that pattern. It still needs the Pendulum Summon procedure and Pendulum Zone effects, but it is placed into a Pendulum Zone by its own effect instead of being activated from the hand as a regular Pendulum Card.

Pendulum Zone Effects

Use LOCATION_PZONE for effects that belong to the Pendulum Zone:

local e1=Effect.CreateEffect(c)
e1:SetType(EFFECT_TYPE_FIELD)
e1:SetRange(LOCATION_PZONE)
e1:SetCode(EFFECT_CANNOT_SPECIAL_SUMMON)
e1:SetProperty(EFFECT_FLAG_PLAYER_TARGET+EFFECT_FLAG_CANNOT_DISABLE+EFFECT_FLAG_CAN_FORBIDDEN)
e1:SetTargetRange(1,0)
e1:SetTarget(s.splimit)
c:RegisterEffect(e1)

D/D Savant Kepler (c11609969.lua) uses this kind of effect to restrict Pendulum Summons, then another Pendulum Zone effect to update its scales during the Standby Phase.

Even though the core stores Pendulum Zone cards inside the Spell & Trap Zone structure internally, scripts should still use the Pendulum Zone API for Pendulum-specific checks:

Need	Use
Effect only applies in a Pendulum Zone	SetRange(LOCATION_PZONE)
Read the left or right Pendulum Zone card	Duel.GetFieldCard(tp,LOCATION_PZONE,0) or Duel.GetFieldCard(tp,LOCATION_PZONE,1)
Count Pendulum Zone cards	Duel.GetFieldGroupCount(tp,LOCATION_PZONE,0)
Check whether a Pendulum Zone is open	Duel.CheckLocation(tp,LOCATION_PZONE,0) or Duel.CheckLocation(tp,LOCATION_PZONE,1)
Move a Pendulum Card to a Pendulum Zone	Duel.MoveToField(tc,tp,tp,LOCATION_PZONE,POS_FACEUP,true)

Use LOCATION_SZONE for ordinary Spell & Trap Zone effects. Use LOCATION_PZONE when the card text or mechanic specifically means a Pendulum Zone.

Scale Checks

The shared Pendulum Summon condition reads the left Pendulum Zone card as the procedure handler and the right Pendulum Zone card as the partner scale:

local rpz=Duel.GetFieldCard(tp,LOCATION_PZONE,1)
local lscale=c:GetLeftScale()
local rscale=rpz:GetRightScale()
if lscale>rscale then lscale,rscale=rscale,lscale end

Then each candidate monster must have a Level strictly between the two scales:

lv>lscale and lv<rscale

The endpoints are not included. With scales 1 and 8, Level 2 through Level 7 can pass the scale check; Level 1 and Level 8 cannot.

Performapal Popperup (c11481610.lua) shows the same manual pattern in a Spell effect. It reads both Pendulum Zone cards, swaps the values if needed, then checks hand monsters against lv>lsc and lv<rsc.

Use the current scale getters when runtime scale changes matter:

local lpz=Duel.GetFieldCard(tp,LOCATION_PZONE,0)
local rpz=Duel.GetFieldCard(tp,LOCATION_PZONE,1)
if not lpz or not rpz then return false end

local lscale=lpz:GetLeftScale()
local rscale=rpz:GetRightScale()
if lscale>rscale then lscale,rscale=rscale,lscale end

Card.GetLeftScale and Card.GetRightScale return modified current values while the card is in a Pendulum Zone. D/D Savant Kepler updates both scales with EFFECT_UPDATE_LSCALE and EFFECT_UPDATE_RSCALE, so current scale reads are the right habit for live gameplay checks.

Use Card.GetOriginalLeftScale and Card.GetOriginalRightScale only when the text specifically cares about printed/original scale values.

Pendulum Summon Candidate Pool

The shared helper builds the possible locations from the zones the player can use:

local loc=0
if Duel.GetLocationCount(tp,LOCATION_MZONE)>0 then
    loc=loc+LOCATION_HAND
end
if Duel.GetLocationCountFromEx(tp,tp,nil,TYPE_PENDULUM)>0 then
    loc=loc+LOCATION_EXTRA
end

That means:

Source	Why it may be included
Hand	There is at least one usable Monster Zone for monsters from the hand.
Extra Deck	There is at least one legal zone for a face-up Pendulum Monster from the Extra Deck.

The candidate itself still has to pass Auxiliary.PConditionFilter. The local helper checks that the card:

• is in the hand, or is face-up and is a Pendulum Monster
• has a Level between the two active scales
• can be Special Summoned with SUMMON_TYPE_PENDULUM
• is not forbidden
• can be included under the regular or extra Pendulum Summon count currently being used

Local procedure.lua also checks c.pendulum_level before falling back to c:GetLevel(). That is a procedure-backed compatibility hook for cards whose Pendulum Summon Level is stored on the card table instead of coming from the ordinary Level getter.

Selection And Resolution

Pendulum Summon selection has to respect three counts:

Count	Local variable	Meaning
Main Monster Zone count for hand monsters	ft1	How many selected cards may come from the hand.
Extra Deck summon count for face-up Extra Deck Pendulum Monsters	ft2	How many selected cards may come from the Extra Deck.
Total usable Monster Zones	ft	The total size limit for the selected group.

The helper uses Auxiliary.PendOperationCheck(ft1,ft2,ft) as a Group.SelectSubGroup check. It splits the candidate group into Extra Deck and non-Extra Deck cards, then refuses selections that exceed any of those three limits.

Inside the normal shared procedure, the operation does not call Duel.SpecialSummon directly. It merges the selected cards into the group given by the core:

sg:Merge(g)

The core's EFFECT_SPSUMMON_PROC_G path then filters the group again, handles Special Summon costs, assigns SUMMON_TYPE_PENDULUM, moves each selected monster to the Monster Zone, and announces the Summons.

When you are writing a normal Pendulum Monster, let aux.EnablePendulumAttribute handle that flow. Do not try to duplicate it with a manual Duel.SpecialSummon call.

Extra Pendulum Summons

The shared helper tracks the regular once-per-turn Pendulum Summon in Auxiliary.PendulumChecklist. At the start of each Draw Phase, Auxiliary.PendulumReset clears the checklist.

If the regular Pendulum Summon has already been used, the helper only allows a new Pendulum Summon if the player is affected by an EFFECT_EXTRA_PENDULUM_SUMMON effect. When both a regular and an extra Pendulum Summon are available, the operation offers the player a choice. If an extra effect is chosen, the helper calls that effect's value filter and then uses its count limit with:

ce:UseCountLimit(tp)

Pendulum Evolution (c55795155.lua) shows a scripted extra Pendulum Summon. It temporarily registers an EFFECT_EXTRA_PENDULUM_SUMMON, reads both Pendulum Zones, builds the candidate locations, reuses aux.PConditionFilter, and uses aux.PendOperationCheck for selection limits.

That script performs its own Duel.SpecialSummon because the Spell effect is not the standard Pendulum Monster procedure. For ordinary Pendulum Monsters, prefer the shared helper and let the core perform the group procedure.

Moving Cards To A Pendulum Zone

Use Duel.CheckLocation before activating an effect that must place a card in a Pendulum Zone:

function s.pentg(e,tp,eg,ep,ev,re,r,rp,chk)
    if chk==0 then
        return Duel.CheckLocation(tp,LOCATION_PZONE,0)
            or Duel.CheckLocation(tp,LOCATION_PZONE,1)
    end
end

Then recheck relation and move the card during resolution:

function s.penop(e,tp,eg,ep,ev,re,r,rp)
    local c=e:GetHandler()
    if c:IsRelateToEffect(e) then
        Duel.MoveToField(c,tp,tp,LOCATION_PZONE,POS_FACEUP,true)
    end
end

Supreme King Z-ARC uses exactly this pattern after it is destroyed face-up from the Monster Zone. Chronograph Sorcerer (c12289247.lua) and Astrograph Sorcerer, the Star Magician (c48171151.lua) use the same movement function to place selected Pendulum Cards from the hand or Deck into a Pendulum Zone.

The local core accepts LOCATION_PZONE in Duel.MoveToField. Internally it maps the destination to the Spell & Trap Zone with a Pendulum Zone flag, then lets the player choose an open Pendulum Zone. If no Pendulum Zone is usable, the core sends the card to the GY by rule and the move does not succeed.

Advanced placement effects can pass the optional seventh zone argument. For Pendulum Zone moves, the low bits are used:

Zone argument	Pendulum Zone allowed
omitted or 0xff	either Pendulum Zone
0x1	left Pendulum Zone only
0x2	right Pendulum Zone only
0x3	either Pendulum Zone

Most local scripts omit the seventh argument and let the player choose any available Pendulum Zone.

Revive-Limit Pendulum Summonable Monsters

Some Pendulum Monsters are also Special Summon Monsters. They need revive-limit handling, but their text may still allow them to be Pendulum Summoned from a specific location.

Odd-Eyes Revolution Dragon (c16306932.lua) uses:

aux.EnablePendulumAttribute(c)
aux.EnableReviveLimitPendulumSummonable(c,LOCATION_HAND)

The second helper does three things in local procedure.lua:

1. Calls c:EnableReviveLimit().
2. Stores the allowed Pendulum Summon locations as psummonable_location.
3. Registers a continuous EVENT_SPSUMMON_SUCCESS effect that calls c:CompleteProcedure() if the card was Pendulum Summoned.

That is why the Pendulum condition can pass special nocheck and nolimit values into IsCanBeSpecialSummoned only when Auxiliary.PendulumSummonableBool(c) says the card is in one of its allowed locations.

Use this helper for Special Summon Monsters that are allowed to be Pendulum Summoned despite having revive-limit rules. Do not call CompleteProcedure manually for every ordinary Pendulum Monster.

Scale-Based Effects

Some cards do not perform a Pendulum Summon but still inspect scales. Pendulum Scale (c17885118.lua) requires two cards in your Pendulum Zones, reads the left card's left scale and the right card's right scale, then chooses different outcomes based on the absolute difference:

local tc1=Duel.GetFieldCard(tp,LOCATION_PZONE,0)
local tc2=Duel.GetFieldCard(tp,LOCATION_PZONE,1)
local scl1=tc1:GetLeftScale()
local scl2=tc2:GetRightScale()
local dif=math.abs(scl1-scl2)

This is a good pattern for effects that care about the active Pendulum Scale pair but are not themselves Pendulum Summons. Guard that both Pendulum Zones are occupied before reading the cards, then use the scale getters that match the text.

Common Pitfalls

Mistake	Better habit
Forgetting aux.EnablePendulumAttribute(c) on a normal Pendulum Monster.	Put it near the top of initial_effect, before Pendulum Zone and monster effects.
Adding a custom activation effect but leaving the default helper activation in place.	Use aux.EnablePendulumAttribute(c,false) when the card should not get the default hand activation effect.
Using LOCATION_SZONE for a Pendulum Zone effect.	Use LOCATION_PZONE for Pendulum Zone effects and Pendulum Zone checks.
Treating scale endpoints as legal Levels.	Check Levels strictly between the two scales: lv>low_scale and lv<high_scale.
Assuming the left scale is always lower.	Read both scales and swap them before comparing Levels.
Trying to Pendulum Summon face-down cards from the Extra Deck.	The shared helper only accepts face-up Pendulum Monsters from the Extra Deck path.
Checking only total Monster Zone space.	Respect hand capacity, face-up Extra Deck capacity, and total usable Monster Zones.
Calling Duel.SpecialSummon inside an ordinary Pendulum Monster's procedure.	Let aux.EnablePendulumAttribute and the core group procedure resolve the Summon.
Moving a card to a Pendulum Zone without checking open zones.	Use Duel.CheckLocation(tp,LOCATION_PZONE,0/1) before activation and relation checks during resolution.
Forgetting revive-limit completion for Special Summon Monsters that can be Pendulum Summoned.	Use aux.EnableReviveLimitPendulumSummonable(c,loc) for that specific pattern.

Useful API Pages

• Auxiliary.EnablePendulumAttribute
• Auxiliary.PendCondition
• Auxiliary.PendOperation
• Auxiliary.PendOperationCheck
• Auxiliary.PendulumReset
• Auxiliary.PendulumSummonableBool
• Auxiliary.EnableReviveLimitPendulumSummonable
• Auxiliary.PSSCompleteProcedure
• Card.GetLeftScale
• Card.GetRightScale
• Card.GetOriginalLeftScale
• Card.GetOriginalRightScale
• Card.GetCurrentScale
• Card.IsCanBeSpecialSummoned
• Card.EnableReviveLimit
• Card.CompleteProcedure
• Card.IsSummonType
• Duel.GetFieldCard
• Duel.GetFieldGroup
• Duel.GetFieldGroupCount
• Duel.CheckLocation
• Duel.GetLocationCount
• Duel.GetLocationCountFromEx
• Duel.GetUsableMZoneCount
• Duel.MoveToField
• Duel.SpecialSummon
• Effect.UseCountLimit
• Group.SelectSubGroup