Forced

Forced refers to compulsory game effects that must be resolved.

Details
For example, both of the above card includes the text of する (Suru) meaning "To do" in the card text of their destroy effect.

If the card is used, certain actions must be used. It usually doesn't matter, but if your opponent was controlling a single creature such as Red ABYTHEN Kaiser in the battle zone, you would be forced to choose it when you put Thunder Blade into the battle zone, and you will lose the cards in your mana zone. Attention should be paid to card abilities that are forced and your opponents cards that have negative results when they are chosen as a target.


 * There is a forced "rewind" process at the start of the game, regarding the untap step. If you carelessness forgot about it, it rewinds back to that step. This should be avoided in tournament play however, as warnings will be given out.
 * If more than one Substitution Effect will replaced the same event, you may choose either. It doesn't matter whether the choice is optional or forced.
 * If Lupia Lapia is destroyed while crossed with Spiral Aura, you may choose to return Lupia Lapia to your mana zone with its optional effect by returning a dragon to your hand, or you may return it to your hand with the effect of Spiral Aura.

If there are multiple substitution effects that can be applied to the same event, but the owner of those cards is different, apply from the active player.
 * For example, if you try to break a shield that is fortified by Silver Glory, Invincible Fortress with Bolmeteus Steel Dragon, the substitution effect of Bolmeteus takes precedence and the substitution effect of Silver Glory doesn't apply. Other shields can't be replaced and are put into the graveyard.

When a a card "prohibiting an action" and "forcing an action" are simultaneously applied, the prohibition takes precedence.
 * Even if you cast Forced Frenzy while Nariel, the Oracle in the battle zone, creatures that have power 3000 or more can't attack.
 * If your opponent has Codeking Number Nine in the battle zone, you can't cast spells with Bluum Erkis, Flare Guardian.

It is the opposite of Optional. If a card says "if you do", you may choose not to use an ability.