Control-Switch Effects: "Unaffected" Is a Legal Target, "Control Cannot Switch" Is Not

Two monsters can both end up not changing sides from a control-switch effect, yet the game treats them completely differently for activation/selection legality:

• A monster whose own text says its control cannot switch (e.g. Blindly Loyal Goblin) is an illegal selection for a control-change effect. A pure control-change effect cannot be activated/targeted if this is the only monster available.
• A monster that is merely unaffected by the relevant effects (a "towers" monster) is a fully legal selection. The control-change effect can be activated and can legally pick it; the swap/take just produces no result because the monster is unaffected.

The deciding question is not "will control actually switch?" It is "does the game recognize this monster's control as switchable?" Only explicit "control … cannot switch/change" text makes the answer no. This is the control-switch companion to Unaffected Is Not Cannot-Be-Targeted.

Control-change targets the card, never "the player"

A control-change effect acts on the card itself, despite wording that sounds like it acts on a player. The game's selection check therefore reads the card's properties:

• If the card carries a "control cannot switch" lock, it is not a legal control-change selection at all.
• If the card is only unaffected by [Spell/card] effects, nothing about it is flagged as unswitchable. It is a normal, legal selection. "Unaffected" suppresses the applied result at resolution; it does not retroactively make the monster an illegal pick. ("Unaffected" ≠ "cannot be targeted" — see ruling 33.)

Change of Heart — "Target 1 monster your opponent controls; take control of it until the End Phase." Per the OCG 7/4/24 update, Change of Heart cannot target an Armed Dragon Thunder LV10 while its "● 10+: Control of it cannot switch" is applying — a text lock makes it an illegal target. But Change of Heart can target a monster that is merely unaffected by Spell effects (legal target; control is simply not taken at resolution).

Graydle Alligator — its control-take effect can still equip to a Botanical Lion whose "Control of this face-up card on the field cannot switch" is applying: "you cannot take control… but the effect that destroys it when Graydle Alligator leaves the field will still apply." The lock blocks the control-take result, not the rest of the effect.

Creature Swap: blocked only by a text lock, not by "unaffected"

Creature Swap (Normal Spell) — "Each player chooses 1 monster they control and switches control of those monsters with each other. Those monsters cannot change their battle positions for the rest of this turn."

Creature Swap does not target; each player chooses at resolution. It needs each player to control an eligible monster — "eligible" meaning the game allows it to be selected for a control switch, i.e. it is not under a "control cannot switch" lock. Apply the distinction above:

• Only monster is text-control-locked (Blindly Loyal Goblin: "As long as this card remains face-up on the field, control of this card cannot switch") → it is not an eligible selection → if it is a player's only monster, neither player can activate Creature Swap. (Official TCG ruling: "Neither player can activate Creature Swap if the only monster you control is Blindly Loyal Goblin.")
• Only monster is merely unaffected by Spell effects (a "towers" monster) → it is an eligible selection. Creature Swap CAN be activated, the player can choose that monster, but the mutual swap is impossible to apply, so Creature Swap resolves without effect — neither monster switches (the exchange is all-or-nothing). It is not an activation block.

A player may select their unaffected monster for the swap even while controlling another normal monster — the unaffected monster was always a legal swap target. Skill Drain illustration: summon a "towers" monster whose immunity comes from its own effect, with Skill Drain face-up negating that effect. Its protection is off, but from Creature Swap's activation-legality view nothing changed — the monster was a legal swap target before (unaffected, swap fizzles) and is a legal swap target now (no longer unaffected, swap actually works). "Unaffected" was never an activation factor.

Raigeki contrast — no selection requirement at all

Raigeki (Normal Spell) — "Destroy all monsters your opponent controls."

Raigeki selects nothing; it applies one bulk result to a group. It needs only that the opponent control a monster.

• Opponent's only monster is unaffected by Spell effects → Raigeki activates; that monster survives (result suppressed). Same net outcome as Creature Swap here — both activate and both leave the unaffected monster in place.
• Opponent's only monster is text-control-locked (Blindly Loyal Goblin) → Raigeki activates and destroys it. A control lock is not destruction immunity. This is the one board where Raigeki and Creature Swap genuinely diverge: Raigeki still wipes it, while Creature Swap can't even be activated against it as the only monster.

Worked example — the reported scenario, corrected

The opponent's only monster is unaffected by Spell effects. Why does Raigeki work but Creature Swap not?

— Answer: They don't actually differ here — both can be activated, and neither affects the unaffected monster. Raigeki activates and the monster simply isn't destroyed. Creature Swap can also be activated: an unaffected monster is a legal swap selection (it is not the same as "control cannot switch"); the swap just resolves without effect. The claim that Creature Swap is illegal to activate against an unaffected monster is wrong. Creature Swap is only un-activatable when a player's only monster is under an explicit "control cannot switch" lock (e.g. Blindly Loyal Goblin) — and on that board Raigeki would still activate and destroy it.

Judge calls to watch for

• Do not rule Creature Swap (or any control-switch effect) un-activatable just because a chosen monster is unaffected. Unaffected monsters are legal selections; the effect activates and the swap/take fizzles at resolution. Activation is not blocked.
• Creature Swap's activation is blocked only when a player's only monster carries explicit "control cannot switch/change" text (Blindly Loyal Goblin). That is a true ineligible selection.
• Change of Heart-style pure control-take cannot target a text-control-locked monster (OCG 7/4/24), but can target an unaffected one (control just isn't taken). Same split as Creature Swap.
• Control-change acts on the card, not the player; selection legality is read off the card's lock text, not off whether the swap will succeed.
• A control lock is not destruction immunity: Raigeki/Dark Hole still destroy Blindly Loyal Goblin.
• A monster made unaffected by its own effect is still a legal swap target; negating that effect (Skill Drain) changes whether the swap works, not whether Creature Swap can be activated.

Sources

• OCG 7/4/24 rulings update (YGOrganization): Change of Heart cannot target Armed Dragon Thunder LV10 under "Control of it cannot switch"; Graydle Alligator can still equip a Botanical Lion with "control of this card cannot switch" but cannot take control. https://ygorganization.com/ocg-7-4-24-rulings-update/
• Creature Swap TCG rulings (Yugipedia): "Creature Swap does not target"; "both players must have at least 1 eligible monster… to be activated"; Blindly Loyal Goblin — "Neither player can activate Creature Swap if the only monster you control is Blindly Loyal Goblin." https://yugipedia.com/wiki/Card_Rulings:Creature_Swap
• "Unaffected" is a legal target/selection, not a control lock — see ruling 33.
• Verbatim card text (Creature Swap, Raigeki, Change of Heart, Blindly Loyal Goblin) via YGOPRODeck API.