Several of the standard NwN game mechanics have been altered in order to preserve balance between the several classes of the game on City of Arabel. They are listed as follows.
- Many classes have had their abilities tweaked. The changes are listed here.
- Many spells on CoA have been tweaked for balance reasons, they are listed here.
- Familiars are greatly reduced in power. They have had removed their damage reduction, their regeneration, and spell like abilities. They have penalties to skills they were given for the OC, like Disable Device and Open Lock.Familiars were also modified to have a new appearance.
- Armor and armor enhancement bonuses have been 'merged' through scripting. Mage armor, bracers of armor, and both the base and bonus part of armor is supposed to be all one type, and will be treated as such by the engine now. So if you had leather armor +1, bracers of armor AC3, and mage armor all running, you'd only be at +4 AC total, because all those sources overlap. Other types are still cumulative, like natural, deflection, and dodge. (And of those, dodge stacks, the others overlap similar bonuses of the same type.)
- The time a game hour lasts has been doubled to four minutes. This means hour/level spells are much more useful than the turn/level spells now.
- Multiple items with the same ability score or skill bonus will no longer stack, nor will any spell that grants ability score bonuses stack with items.
- You get a dodge AC bonus from tumble only if your modified tumble is at least as high as your trained ranks in tumble.