>>20941696I didn't think about how Giratina itself would be affected, and you're right.
What else could it be? I'd like to see a better version of Shadow Tag that also damages all non-Ghost pokémon over time, but that sounds like something only a pure evil legendary would have. Even a god of the dead (which Giratina isn't as far as I know) wouldn't necessarily have any inherent power over the fates of the living.
If only there was a Ghost Terrain move the choice would be obvious.