Only while visible is an accessibility limitation found on H79 for an Affliction used by the Howler variant of the Phantasm port of the Ghost.
A phantasm is at base an Apparition (H78) which is a Ghost with Always-On Insubstantiality.
- Ghosts are a variant of Spirit (B263) who still have the baseline "Usually On" enhancement of Invisibility.
The implication being here that they need to spend 1 FP/second to turn visible to be able to launch their Affliction.
This wouldn't be much of a limitation for beings who could not normally turn invisible anyway, as they would always be fulfilling their accessibility except for strange circumstances which give them powers.
One approach for this would be Alternative Abilities but the problem there is it is only available for fully-switchable abilities, which "Usually On" powers are not.