The first alteration is a very slight one. As well as the elements having their Everwayan meaning they carry a secondary meaning as well. Fire is Physical Attack strength, Earth is Physical Defence strength, Air is Magical Attack strength and Water is Magical Defence strength.
The second is rather major, there is no Spherewalking or gates of any kind. So the PCís are not Spherewakers. They are just characters in a world.
Thirdly is the introduction of jobs, and their effect on powers, and the abolishment of magic as given in the rules in Everway. Magic in Final Fantasy is quite different, and needed to be handled in a different manner. Details on these are found here.
Fourthly is the system of elements. There are 4 elements of magic in Final Fantasyway which are different to the elements of the statistics. These are Fire, Water, Thunder and Ice. Every creature has an element (with a few exceptions) and some attacks, magic or weapons can have elements. Attacking a creature with its own element will only help it. However attack it with its opposing element and you will hurt it greatly. Fire is strong against Ice, Ice is strong against Thunder, Thunder is strong against Water, and Water is strong against Fire. Taking that the other way should give you the weaknesses. Attacking with an element that is neither strong nor weak is considered a normal attack. As is a non-elemental attack, or an elemental attack against a non-elemental foe.
Fifthly is a system of riding. Any creature in the world of Gaia could be theoretically ridden, but a simple rule applies, a creature will only let you ride it if you can easily best it in battle. In general this means if your Fire score is greater than theirs, or for Black Mages if their Air is greater than the monsters Fire. If equal you might be able to get on the beast, but it will try and buck. If less youíre just going to get seriously hurt. Of course some creatures might voluntarily let you ride them, and some are trained to be mounts and pack animals (Shoopufs and Chocobos). Use common sense here please, no-one is going to be able to ride around on Ramuh or a Moogle.
Finally I should state that this is more combat oriented than Everway, hence the fact Iím working to help clarify the combat system, look here for the current version. Combat tends to be more involved, taking more actions and draws to resolve it, which monsters and characters alike using various skills to help themselves and hinder their enemies. If you donít want to fight gigantic monsters and nefarious sorcerers this is probably not for you. On the plus side a game could be just a very quick combat mission, so it can be great for short sessions. I suggest for now the following rules for combat. At the start of combat compare everyoneís Fire scores. The character with the highest Fire gets to go first, the second highest second and so on. Each character gets to perform one action or activate one power. Resolve the use of this before moving on to the next character. To resolve an action compare the attackers Fire score to the defenders Earth score. If the Fire is greater the attack is successful and damage will be done (the amount of damage depends of the difference). If equal I suggest you draw a card to decide the outcome, with a favourable draw always working in the PCís favour. Magic replaces this with Air and Water scores. Combat ends when one side is either completely immobilised or knocked unconscious, or if one side runs away.