Optional

Optional refers to non-compulsory effects of cards that don't need to be used.

Details

For example, if you know your opponent has a Death Gate, Gate of Hell in his hand, you can choose not to untap your Urth, Purifying Elemental in order to avoid the Death Gate.

Although the Heavens Gate has an effect that tells you to put 2 creatures into the battle zone, as the choice is "up to", you may choose 0 cards and it acts as optional. This is also true for cards that tell you to "choose a number".

• 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.

The "if you do" or "you may" can cover a single event in a sentence of text. This is seen on the newer text of Maeterl, Beautiful Sunday.

Cost Trampling effects from non-public information such as shields or deck is treated as optional, even if its written as being forced "put into the battle zone". For example, even if you look at the shields with the ability of Codefight Agatha Hercule, you can choose not to play spells For No Cost.

It is the opposite of Forced. If a card says "To Do", you must use an ability.