Momentary "When Summoned" Locks and Chain Resolution Order

Some cards stop the opponent from acting "when" a specific event happens — e.g. Branded Lost's "your opponent cannot activate cards or effects when a monster is Fusion Summoned this way," or similar "when this card is Special Summoned, your opponent cannot activate cards or effects" clauses. These are momentary windows tied to a single timing, not a lingering status the controller carries for the rest of the chain or turn. Their reach depends on where in the chain the triggering event resolves.

The mechanic

• No player has priority during chain resolution. Chain Links resolve one after another with no chance to respond in between. So a "when X happens, opponent cannot activate" lock can only ever matter at the next point the opponent could act — the response window that opens after the current chain finishes resolving.
• That post-chain window only counts as the locked "when X" window if X was the last (or only) thing to resolve. If other effects resolve after X in the same chain, the window the opponent eventually gets belongs to those later effects, and the "when X" lock has already lapsed.
• Chain Links resolve in reverse order (LIFO): the last link activated resolves first; the first link activated resolves last. So putting the locking effect earlier in the chain (a lower Chain Link) buries its event mid-resolution and weakens its own lock.

Worked example — Branded Lost whiffs

You control Branded Lost.

1. Activate Pot of Greed — Chain Link 1.
2. Chain Super Polymerization — Chain Link 2.

Resolution (LIFO):

• CL2 Super Polymerization resolves first → the Fusion Summon happens here, mid-chain. No one has priority.
• CL1 Pot of Greed resolves last → draw 2.
• Chain ends; the opponent now gets a response window — but it follows Pot of Greed's resolution, not the Fusion Summon.

Result: Branded Lost's "when a monster is Fusion Summoned" lock has already lapsed. The opponent may activate Torrential Tribute, Bottomless Trap Hole, Forbidden Chalice, etc. on the freshly summoned monster.

Contrast: activate Super Polymerization alone (or as the highest Chain Link with nothing resolving after it). The Fusion Summon is the last thing to resolve, the immediate post-resolution window is the "when Fusion Summoned" window, and the lock holds.

Practical rule

To keep a momentary "when [event]" lock live, the locking event must be the final thing that resolves on the chain. Do not bury it under a later-resolving Chain Link. When the controller wants the lock, they should resolve the locking effect last (activate it on the lowest Chain Link, or on its own chain).

Don't confuse with "in response to this card's activation"

A different, broader protection reads "neither player can activate cards or effects in response to this card's activation" (e.g. Super Polymerization itself, Forbidden Droplet). That closes the activation window — nothing can chain to the card at all — and is unaffected by where the eventual summon resolves. Keep it separate from a "when [event]" lock, which only governs the post-resolution window for that event. A card can have both, and they cover different moments. See Branded Lost and Chain Resolution.

Judge guidance

• A "when X happens, opponent cannot activate" clause is timing-scoped, not a status. Ask where X resolves in the chain before ruling the opponent locked.
• If anything resolves after the triggering event in the same chain, treat the opponent as not locked for the post-chain window.
• Distinguish this from activation-window locks ("in response to this card's activation"), which do not depend on resolution order.