Control Change

Changing control means the card stays on the field but its controller changes. Do not move the card manually with a send or summon function. Use the control APIs so the engine can update zones, control-change resets, equipment state, and effect checks.

The Basic Take-Control Shape

Change of Heart (c4031928.lua) is the small baseline:

lua

function s.target(e,tp,eg,ep,ev,re,r,rp,chk,chkc)
    if chkc then
        return chkc:IsLocation(LOCATION_MZONE)
            and chkc:IsControler(1-tp)
            and chkc:IsControlerCanBeChanged()
    end
    if chk==0 then
        return Duel.IsExistingTarget(Card.IsControlerCanBeChanged,tp,0,LOCATION_MZONE,1,nil)
    end
    Duel.Hint(HINT_SELECTMSG,tp,HINTMSG_CONTROL)
    local g=Duel.SelectTarget(tp,Card.IsControlerCanBeChanged,tp,0,LOCATION_MZONE,1,1,nil)
    Duel.SetOperationInfo(0,CATEGORY_CONTROL,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.GetControl(tc,tp,PHASE_END,1)
    end
end

Duel.GetControl changes control to the given player. PHASE_END,1 makes the control change temporary until the End Phase. Omit those arguments for a permanent control change.

Legality Checks

Use the local control helpers instead of hardcoding your own rule list.

Check	Common use
`Card.IsControlerCanBeChanged`	A direct take-control target. It includes Monster Zone availability unless told to ignore it.
`Card.IsAbleToChangeControler`	A broader "this card may change control" check, useful before swap-control logic.
`Duel.GetMZoneCount`	Manual zone-space checks, especially for swaps where each player will receive a card.

The API uses the engine spelling Controler in function names. In prose, use "controller".

Use The Return Value

Duel.GetControl returns the number of cards whose control actually changed. Mind Control (c37520316.lua) uses that return before adding the attack and Tribute restrictions:

lua

if tc:IsRelateToEffect(e) and Duel.GetControl(tc,tp,PHASE_END,1)~=0 then
    local reset=RESET_EVENT+RESETS_STANDARD+RESET_PHASE+PHASE_END
    local e1=Effect.CreateEffect(c)
    e1:SetType(EFFECT_TYPE_SINGLE)
    e1:SetCode(EFFECT_UNRELEASABLE_SUM)
    e1:SetReset(reset)
    e1:SetValue(1)
    tc:RegisterEffect(e1)
    local e2=e1:Clone()
    e2:SetCode(EFFECT_UNRELEASABLE_NONSUM)
    tc:RegisterEffect(e2)
    local e3=e1:Clone()
    e3:SetCode(EFFECT_CANNOT_ATTACK)
    tc:RegisterEffect(e3)
end

That matters because the follow-up restrictions only make sense if the monster actually came under your control.

Swap Control

Swap effects need two cards and enough Monster Zone space after both cards leave their current zones. Mind Castlin (c12172567.lua) checks both sides with LOCATION_REASON_CONTROL:

lua

function s.swapfilter(c)
    local tp=c:GetControler()
    return c:IsAbleToChangeControler()
        and Duel.GetMZoneCount(tp,c,tp,LOCATION_REASON_CONTROL)>0
        and c:IsFaceup()
end

Its operation then swaps the handler with the selected opponent's monster:

lua

function s.operation(e,tp,eg,ep,ev,re,r,rp)
    local tc=Duel.GetFirstTarget()
    local c=e:GetHandler()
    if c:IsRelateToEffect(e) and tc and tc:IsRelateToEffect(e) then
        Duel.SwapControl(c,tc)
    end
end

Duel.SwapControl can also take reset phase/count arguments for temporary swaps.

Continuous Control From Equip Cards

Some cards do not call Duel.GetControl after activation. They equip to the monster, then apply a continuous equip effect that sets the controller.

Comic Hand (c33453260.lua) equips to an opponent's monster and registers:

lua

local e3=Effect.CreateEffect(c)
e3:SetType(EFFECT_TYPE_EQUIP)
e3:SetCode(EFFECT_SET_CONTROL)
e3:SetValue(s.cval)
c:RegisterEffect(e3)

function s.cval(e,c)
    return e:GetHandlerPlayer()
end

That is an equip relationship. If the Equip Card stops applying or leaves the field, the continuous control rule stops applying too.

Owner And Controller

Control changes do not change ownership. The owner is the player whose card it is; the controller is the player currently controlling it.

Use the right question:

Question	Function
Who controls this card right now?	`Card.GetControler`
Is this card currently controlled by player `p`?	`Card.IsControler`
Who owns this card?	`Card.GetOwner`

Most take-control effects care about current controller. Some immunity or ownership-based text cares about owner instead.

Common Mistakes

Mistake	Better pattern
Sending a monster to another zone to represent control change.	Use `Duel.GetControl` or `Duel.SwapControl`.
Forgetting Monster Zone space.	Use `Card.IsControlerCanBeChanged` for direct take-control effects or `Duel.GetMZoneCount` for swaps.
Adding follow-up restrictions even when control did not change.	Check `Duel.GetControl(...)~=0`.
Using owner checks when the text cares about current control.	Use controller functions for "your opponent controls" and owner functions for ownership text.
Targeting a monster that cannot change control.	Put `IsControlerCanBeChanged` or `IsAbleToChangeControler` in the target filter.
Treating equip-based control like a one-time control change.	Use `EFFECT_SET_CONTROL` on the Equip Card when the control is maintained by the equip relationship.

Useful API pages:

Control Change ​

The Basic Take-Control Shape ​

Legality Checks ​

Use The Return Value ​

Swap Control ​

Continuous Control From Equip Cards ​

Owner And Controller ​

Common Mistakes ​