Cthulhu Wars
Are Ongoing abilities optional, or do they always apply?
The rulebook's Special Abilities section states the optional rule and the exception for abilities whose text says otherwise.
- Cthulhu Wars rulebook · Rulebook · Special Abilities and Spellbooks
Yes, they are optional by default. The rulebook says spellbooks, Great Old One abilities and unique faction abilities, including Ongoing abilities, may be declined at the moment they would take effect. The exception is an ability whose own text says it must take effect.