Half-celestial / half-fiend combined stats or just the better of the 2?

[eyebreaker7]

If you make a half-celestial/half-fiend would they get both stat bonuses or just the better from each?

half-celestial: Str +4, Dex +2, Con +4, Int +2, Wis +4, Cha +4
half-fiend: Str +4, Dex +4, Con +2, Int +4, Wis +0, Cha +2

Str +8 or +4?
Dex +6 or +4
Con +6 or +4
Int +4 or +2
Wis +4
Cha +6 or +4

I've got an idea for a half-celestial/half-fiend that is 2 classes but switches depending on the situation. Kinda like a Jekyll + Hyde type deal I guess now that I think about it. I have originally though about a cleric/barbarian that is his cleric class when half-celestial but switches to a barbarian when he changes to his half-fiend side. Maybe a change of involuntary switching during a stressful situation like combat. Have it also voluntary as well. And once the situation is over he has a chance to switch back to his cleric class. The chance to switch back gets better each round.
I think the most difficult part will be figuring skills. Do I try and keep them separate or just combine them? It's all just one mind that just switches sometimes depending on what's going on.

[InvisibleBison]

Ordinarily, a creature that was both a half-celestial and a half-fiend would use both templates' ability adjustments. It sounds like you're creating a character that alternates between being a half-celestial and a half-fiend, though, so I think it would make sense for only one template to be active at a time.

[eyebreaker7]

One thought is to keep the physical stats the same regardless of which half is "current". He doesn't get stronger or anything (except when he uses barbarian rage). The mental stats however might be different with his Int and Cha being different adjustments for race.. Again, back to figuring the skills differently or combined? He's not 2 different people trapped in one body so to speak he just has split personality of a limited sort.

[False God]

If you have both templates (somehow), you get both effects. Though if he's switching back and forth, I'd argue he only benefits from one or the other at any moment.

I'd recommend separate character sheets. Especially since he's effectively two characters(even if not two people) in one body. I'm fairly certain he'd even have different skills, and different skill levels depending on the form, considering they are rather drastically different characters.

Also, when he's raging as a Barbarian, he can't use a large portion of the Cleric's skills anyway, so there wouldn't be much to gain from investing points in them.