Continuous Stat Modifiers

ATK/DEF changes are one of the easiest ways to learn continuous effects because the result is visible immediately. The script shape changes depending on who receives the modifier:

• the handler itself
• cards in a field range
• the equipped monster
• a monster using this card as material

Choose The Modifier Shape

Pick the effect type by asking who receives the modifier.

Receiver	Effect type	Key setters
The handler itself	EFFECT_TYPE_SINGLE	SetCode, SetValue, and usually EFFECT_FLAG_SINGLE_RANGE plus SetRange
Monsters or cards in a zone range	EFFECT_TYPE_FIELD	SetRange, SetTargetRange, optional SetTarget, SetValue
The equipped monster	EFFECT_TYPE_EQUIP	SetCode, SetValue, plus a separate EFFECT_EQUIP_LIMIT
The monster using this card as Xyz Material	EFFECT_TYPE_XMATERIAL	Material effect type, effect code, and value
A temporary boost from an activated effect	Usually EFFECT_TYPE_SINGLE registered during resolution	SetReset is required

The value can be a fixed number or a callback. Use a callback when the amount depends on current cards, Levels, counters, materials, or another changing state.

Pick The Stat Code

The effect code tells the engine what the value means.

Text shape	Common code family	What the value means
"gains/loses 500 ATK"	EFFECT_UPDATE_ATTACK or EFFECT_UPDATE_DEFENSE	Add or subtract from the current stat.
"ATK becomes 0" as an always-on rule	EFFECT_SET_ATTACK or EFFECT_SET_DEFENSE	Set the stat while the continuous rule applies.
"ATK becomes 0 until..." from a resolving effect	EFFECT_SET_ATTACK_FINAL or EFFECT_SET_DEFENSE_FINAL	Set a final temporary value with the reset used by the resolving effect.

Do not use EFFECT_UPDATE_ATTACK for every ATK-related text. If the card says a stat "becomes" a value, look for a matching local script and copy the set-style code family and reset pattern. If the card says it gains or loses an amount, EFFECT_UPDATE_ATTACK or EFFECT_UPDATE_DEFENSE is usually the right family.

Handler-Only Modifier

Use EFFECT_TYPE_SINGLE when the card modifies itself.

local e1=Effect.CreateEffect(c)
e1:SetType(EFFECT_TYPE_SINGLE)
e1:SetCode(EFFECT_UPDATE_ATTACK)
e1:SetValue(500)
c:RegisterEffect(e1)

If the modifier should only apply while the card is in a specific location, add EFFECT_FLAG_SINGLE_RANGE and SetRange.

e1:SetProperty(EFFECT_FLAG_SINGLE_RANGE)
e1:SetRange(LOCATION_MZONE)

Without the range property, SetRange is not the normal way to bind a single continuous stat modifier to a location.

Dynamic Self Modifier

SetValue can receive a function. For many stat modifiers, the callback is called with the effect and the affected card.

local e1=Effect.CreateEffect(c)
e1:SetType(EFFECT_TYPE_SINGLE)
e1:SetProperty(EFFECT_FLAG_SINGLE_RANGE)
e1:SetCode(EFFECT_UPDATE_ATTACK)
e1:SetRange(LOCATION_MZONE)
e1:SetValue(s.atkval)
c:RegisterEffect(e1)

function s.atkval(e,c)
    return Duel.GetMatchingGroupCount(s.filter,c:GetControler(),LOCATION_MZONE,0,nil)*400
end

This shape is used by local scripts for monsters whose ATK depends on other face-up monsters.

Here are common dynamic sources:

function s.levelval(e,c)
    return c:GetLevel()*200
end

function s.oppdragonval(e,c)
    return Duel.GetMatchingGroupCount(s.dragonfilter,c:GetControler(),0,
        LOCATION_MZONE+LOCATION_GRAVE,nil)*500
end

Use the affected card c when the value depends on the card receiving the modifier. Use e:GetHandler() when the value depends on the card providing the modifier.

Value Functions Do Not Receive tp

Continuous value callbacks usually receive (e,c), not the activated-effect callback list. If the value needs a player as a reference, derive it from the effect or the affected card.

function s.val(e,c)
    local tp=e:GetHandlerPlayer()
    return Duel.GetMatchingGroupCount(s.filter,tp,0,LOCATION_MZONE,nil)*500
end

Use e:GetHandlerPlayer() when the card providing the effect defines the reference player. Use c:GetControler() when each affected card should use its own controller. Local c10000020.lua uses c:GetControler() in its stat value because the amount is based on the affected card's controller's hand.

Field Modifier

Use EFFECT_TYPE_FIELD when a card changes other cards in a range.

local e1=Effect.CreateEffect(c)
e1:SetType(EFFECT_TYPE_FIELD)
e1:SetRange(LOCATION_MZONE)
e1:SetTargetRange(0,LOCATION_MZONE)
e1:SetCode(EFFECT_UPDATE_ATTACK)
e1:SetValue(s.val)
c:RegisterEffect(e1)

SetRange says where the handler must be. SetTargetRange says which zones the modifier reaches.

function s.val(e,c)
    return Duel.GetMatchingGroupCount(s.vfilter,e:GetOwnerPlayer(),LOCATION_MZONE,0,nil)*-300
end

Local c10002346.lua uses the field-modifier version of this idea. It applies ATK and DEF updates to the controller's monsters, and the value function reads the handler's current Xyz Material count:

function s.val(e,c)
    return e:GetHandler():GetOverlayCount()*200
end

If the modifier only applies to some cards in the target range, add SetTarget.

e1:SetTarget(s.tg)

function s.tg(e,c)
    return c:IsFaceup() and c:IsSetCard(0x123)
end

Equip Modifier

Equip Cards use EFFECT_TYPE_EQUIP because the affected card is the equipped monster.

local e1=Effect.CreateEffect(c)
e1:SetType(EFFECT_TYPE_EQUIP)
e1:SetCode(EFFECT_UPDATE_ATTACK)
e1:SetValue(800)
c:RegisterEffect(e1)

When the value depends on the Equip Card, read from e:GetHandler().

function s.atkval(e,c)
    return e:GetHandler():GetCounter(0x1)*500
end

When the value depends on the equipped monster, use the affected card c.

function s.eqlevelval(e,c)
    return c:GetLevel()*100
end

Equip modifiers usually belong beside an Equip activation effect and an EFFECT_EQUIP_LIMIT effect. See Equip Spells and Equip Cards.

Xyz Material Modifier

Some cards grant a continuous modifier while they are attached as Xyz Material. Those effects use a material-related effect type such as EFFECT_TYPE_XMATERIAL, combined with the effect code and value that the card grants.

local e1=Effect.CreateEffect(c)
e1:SetType(EFFECT_TYPE_XMATERIAL)
e1:SetCode(EFFECT_UPDATE_ATTACK)
e1:SetValue(500)
c:RegisterEffect(e1)

Dynamic Xyz Material values can read the affected Xyz Monster.

function s.xyzval(e,c)
    return c:GetOverlayCount()*300
end

Always verify material-effect patterns against local scripts for the mechanic you are copying. Material effects are sensitive to the exact effect type and where the engine expects the card to be.

Dynamic Field Modifier

Field modifiers can use the affected card in the same way.

local e1=Effect.CreateEffect(c)
e1:SetType(EFFECT_TYPE_FIELD)
e1:SetCode(EFFECT_UPDATE_ATTACK)
e1:SetRange(LOCATION_MZONE)
e1:SetTargetRange(LOCATION_MZONE,0)
e1:SetTarget(s.rttg)
e1:SetValue(s.rtval)
c:RegisterEffect(e1)

function s.rttg(e,c)
    return c:IsFaceup() and c:IsType(TYPE_RITUAL)
end

function s.rtval(e,c)
    return c:GetLevel()*100
end

The value callback is run for each affected monster, so c is the monster being modified, not necessarily the handler.

Temporary Stat Modifier

When an activated effect creates a temporary modifier, register the new effect on the affected card and give it a reset.

local e1=Effect.CreateEffect(e:GetHandler())
e1:SetType(EFFECT_TYPE_SINGLE)
e1:SetCode(EFFECT_UPDATE_ATTACK)
e1:SetValue(1000)
e1:SetReset(RESET_EVENT+RESETS_STANDARD+RESET_PHASE+PHASE_END)
tc:RegisterEffect(e1)

The reset is not decoration. It is what makes the modifier expire when the card leaves the expected state or the duration ends.

Clone for ATK and DEF

When ATK and DEF use the same range, target, and value, clone the effect and change only the code.

local e2=e1:Clone()
e2:SetCode(EFFECT_UPDATE_DEFENSE)
c:RegisterEffect(e2)

This keeps paired stat modifiers consistent.

Quick Diagnosis

Symptom	Likely issue
Modifier applies everywhere.	Missing EFFECT_FLAG_SINGLE_RANGE or wrong SetRange.
Field modifier hits the wrong side.	Check SetTargetRange and controller-relative ranges.
Equip bonus affects the Equip Card instead of the monster.	Use EFFECT_TYPE_EQUIP.
Temporary bonus never expires.	Add the correct SetReset.
Dynamic value is stale.	Recalculate in the SetValue function instead of storing once.

Useful API pages:

• Effect.SetValue
• Effect.SetTargetRange
• Effect.SetTarget
• Effect.Clone
• Card.RegisterEffect
• Duel.GetMatchingGroupCount
• Effect.GetHandlerPlayer