Arena Battles feature three-way skirmishes where it's every team for himself. The Sage class replaces the Calculator, with a whole new set of abilities.
This mod also introduces a ton of new content into the game as well. It reaches virtually every aspect of the game, tweaking and adjusting it so that more play styles and strategies are viable-instead of, you know, just having Cid do all the work. What do you need the rest of your party for at that point? Final Fantasy Tactics 1.3 address these issues, and then some. I mean, Cid could clear entire fights all by himself. Certain classes (Calculator), certain characters (Cid), and certain skills (Blade Grasp) are just too powerful for their own good. It's a great game, but it has its quirks. I've played a lot of Final Fantasy Tactics over the years, more than I'd care to admit.