The combat in this game is turn-based, and it looks like it'll use an "Action Point" (AP) system, like from the Fallout series, where each character has a pool of action points that dictate how many attacks they can perform in their turn.

Fallout only had melee and weapons (different weapons used different amounts of AP), and the player's total amount of AP was based completely on Agility.

I was thinking about that and got an idea: What if in Original Sin, the AP cost of an action was based on your attributes?

If you have high agility, moving costs fewer AP.

Fred and Julie each have the "Lightning" spell, which they want to use on rain-soaked enemies. Lighting is magic, boosted by Intelligence, and Fred has only 10 Intelligence, so his AP cost for Lightning is 8 points. Julie has 20 Intelligence, so her AP cost for Lightning is 4 points.

Does something like that sound like a good idea? Or would that be too complicated and make viable character choices more limited?

We're still playing around with those numbers, but yes, AP cost and how many APs you have should depend on stats. I agree. At the moment, skills can also level, so they'll cost less APs. Part of the balancing chore.