Okay, I've completed my extensive tests of the Regenerate Spell:

Regenerate heals the target three times if:
- The target of Regenerate is the caster, Roderick, or Scarlett
- If the caster is Madora and the target is Jahan

Regenerate heals the target only twice if:
- Roderick or Scarlett cast it on Madora or Jahan.
- If the caster is Jahan and the target is Madora

Good luck figuring out that one, coders.