plain and simple, alexander is a dungeon and as op described you travel through out weakening the beast, lets say while its stomping towards the destruction of some city, so it would be a challenge on the team to create a dungeon thats moving on the insides as well as outside (would be visually amazing as i picture it could even add the random dungeon paths thing) then once you get to the heart (deep inside) or head (top of a tower) you would fight a weaker manifestation of alexander in humanoid form, I would think the top of the tower would look way better as you looked out to see the city your about to save creating the sense of urgency. could even incorporate the new flying black chocobos to fly from part to part of the giant summon.
