Stuff we didn't know
1. The joke in RPGs is always "what's a giant spider going to do with money?" In Final Fantasy XII, defeated enemies don't drop gil - but that spider might drop its webbing. Now, here's the kicker: you can sell these items back to the bazaar. Once you sell in enough, you'll unlock special items. It's a win-win situation: kill enemies, get crap, sell it back, and use the money to buy secret gear.
2. Final Fantasy VII had the lifestream. Final Fantasy XII has mist. This mythical fog isn't just for atmosphere - it augments the party's magic, through Mist Cartridges, which store it up and dish it out. It's also used to create Nethicite - a magical substance which grants the fearsome armored judges in Ivalice their powers. It even turns some of them into homicidal maniacs, apparently...
3. Speaking of Mist Cartridges, they're more than just a convenient way to store up magical power. In fact, the Mist Cartridges pave the way for Mist Knacks - think Limit Breaks, Overdrives or any other elaborate character-based special attack from the Final Fantasy series. Launching a Mist Knack allows you to follow it up with another - as long as you hit the right button before the timer runs out. You can chain together as many as you can manage; depending on how well you did, you'll get a bonus elemental magic attack at the end.
4. Summoned monsters - called Espers - fight beside you, replacing two of your party members. They operate on a set of rules (similar to the Gambits which govern character actions) that you can't see. If you fight with a certain Esper enough times, you can learn to predict its actions, so it pays to try out your Espers in battle.
5. As a member of the sky pirate clan, hero Vaan gets his hands on a Clan Primer which tracks all of the monsters you can bounty hunt for extra gil. It also contains a page that collects all of the trophies you earn for meeting certain achievements - say, getting a 50-hit chain in battle - that just happens to look a lot like the awesome 2D graphics from the Final Fantasy Tactics games, which the team behind FFXII developed.