In a game that I'm in, the DM has decided to go with a lycan vs. vampire concept, and this has created a few conundrums.
One of the characters in our group is a dragon disciple, and another character is a barbarian. Both of them decided to take the vampire route, but no one is sure what happens with their constitution-increasing abilities. For example, when the barbarian rages, would that increase his charisma, instead of his constitution?
So far as I can find, whenever a creature doesn't have an ability score (such as a construct or an undead or an incorporeal) generally they use another ability score for all purposes the other would cover. For example, undead use their charisma modifier to determine health and fortitude bonuses, as they don't have a constitution score.
QUESTION: When a creature doesn't have an ability score, and that ability score receives an increase from an ability/spell, how does that effect the creature?