Advanced Gameplay FAQ: Optional Monster Effects

Optional Monster Effects are Trigger Effects that don't happen automatically when the trigger condition is fulfilled - the controlling player decides whether to activate it or not. These effects involve cards like "Mystic Tomato", "Peten the Dark Clown" and "Dark Magician of Chaos".

Missing the timing
It's possible to miss the timing with Optional Trigger Effects, unlike Compulsory Trigger Effects. An Optional Effect "misses the timing" when the triggering condition isn't the last effect to happen in the game state, or didn't happen in the last Chain Link in the current chain.

Most of the time, Optional Trigger Effects can be identified by observing the words, "When...you can..." or "If...you can..." in a monster's effect text.

Example 1
Player A controls a "Peten the Dark Clown".
Player A activates "Fissure".
Player B chains to "Fissure", discarding a card to activate "Raigeki Break", targeting Player A's "Peten the Dark Clown".

On resolution, "Raigeki Break" resolves first, destroying "Peten the Dark Clown". His condition has been met, but can't interrupt the Chain. "Fissure" resolves next, destroying one of Player B's monsters. Now the Chain is complete. However, since "Peten the Dark Clown" being sent to the Graveyard was not the last thing to happen, Player A has missed the timing to activate its effect.

Example 2
Player A controls a "Peten the Dark Clown".
Player A Tributes "Peten the Dark Clown" in order to Summon "Summoned Skull".

Tributing monsters with Optional Trigger Effects for a Tribute Summon also prevents their effects from activating. The last thing to happen is the Summon of the Tribute monster, causing the timing window to close immediately.

In Comparison to Compulsory Trigger Effects
Compulsory Trigger Effects will never miss their timing, as they are mandatory. They lack the words "you can" in the effect description, meaning the effect must attempt to activate eventually.

Example 3
Player A controls a "Sangan".
Player A activates "Fissure".
Player B chains to "Fissure", discarding a card to activate "Raigeki Break", targeting Player A's "Sangan".

On resolution, "Raigeki Break" "resolve"s first, destroying "Sangan". His condition has been met, but can't interrupt the Chain. "Fissure" resolves next, destroying one of Player B's monsters. Now the Chain is complete. Since the effect of "Sangan" is mandatory, it activates now, and forms a new Chain with its effect as Chain Link 1.

“If… you can” Vs. “When… you can”
An important thing to note: cards which state “If … you can” cannot miss the timing. Only those which state “When … you can” can miss the timing
Example: "Wind-Up Factory" states “If” rather than “When”. This means that the card just has to look for an instance of its trigger happening, and will wait until the current chain or sequence of events is over before doing something about it. It doesn’t need to be used at the exact moment “When” its trigger is met and just needs to know “If” it happened or not. Such card which state “If” can never miss the timing regardless of how long the preceding chain is.

Simultaneous Optional Trigger Effects
A common question is, "What happens when two Optional Trigger Effects try to activate at the same time?" For example, two copies of "Mystic Tomato" destroy each other in battle. Neither will miss the timing, as the last thing to happen was both being sent to the Graveyard. Both of the effects trigger at the same time, and form a Chain. The Turn Player's effect becomes Chain Link 1, and the opponent's effect becomes Chain Link 2.
Only the activation of an Optional Trigger Effect can miss the timing. In other word, as long as the effect is activated, the resolution will never miss the timing. So two monsters will be summoned in the above example.