Lag, MP shortages and other annoyances.

[Estellios]

For story mode Titan, if people are getting knocked off tell them to watch Titan as well as the floor as he will very visibly turn around to do a Landslide and if you watch him you can see that it is coming maybe a half-second or so before the AOE zone appears.. You can also have people stand right behind him so if they get knocked back they don't get knocked off but it isn't recommended.

Titan is all about conserving your MP as it is likely more AOE than you are used to. Try to get ahold of some Ethers, use them early so that another will be up later in the fight and you will be able to reuse it. A big thing is to remember you have access to Regen now and if your tank is properly geared you usually don't have to worry about them if you Regen them, just avoid casting it on the rest of the party until later in the fight.

Another big way to conserve MP is to use Medica to get people healed up from Titan's stomps. Medica is more efficient if you need to heal 3 or more people. Just make sure your party stays fairly close together. There is no reason to spread out far from each other as the only AOEs you need to be dodging (Landslide), hit the entire arena ( Stomps), and Weight of the Land (Small circle underneath 2 players). Only the latter is dangerous if you bunch up together, so make sure everyone stands near each other but not on top of each other.