A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
Stupid Question Time:
When using this card as a defender to move a unit into the battle, is taking an additional Battle action printed on a card in the unit optional?
Battle: If there are enemy units at the current battlefield: Move one of your target units there. If it moved, straighten it. If you are the Defender, take an additional Battle action printed on a card in the unit.
When using (Doomed Intentions) as a defender to move a unit into the battle, is taking an additional Battle action printed on a card in the unit optional?
No. If there are printed Battle actions, you must use one.
To stave off confusion from others: You can still use the effect when there are no Battle actions printed on cards in the unit, because using the action is an effect, not a cost. The effect will be negated.
But if you can, you must.