Mascot

[wareye]

Will be given by brothers when you have completed an Episode in all places in Spira (excluding Bevelle). what does this mean

[Earl Of Slander]

It means you're going to have to meet all of the requirements in this (http://db.gamefaqs.com/console/ps2/file/final_fantasy_x_2_mascot_speed.txt) guide.

You'll probably have to start a new game.

[AmishOpiate]

The Mascot dress sphere is available in Chapter 5 if you have completed every mission and side quest available. -- taken from generic internet gaming site.

The best, and really only, way to do this, is to get a really good strat guide and follow it through letter by letter, making sure you don't miss anything. It is a lot of work, but Mascot is worth it once you level it up.

EDIT: Adding to what Earl said, I don't know that you have to start a new game, but I would think it would make things easier to keep track of. Some quests like Publicity you have to work on every chapter, so skipping something that you think you have done already could be a disaster.

[Serpentine]

You will have to start a new game if any of the places have an episode concluded because you need an episode complete in all areas except Bevelle.
So unless any place says episode concluded then you shouldn't need to start a new game.

[Earl Of Slander]

Well he wouldn't know if he has an "Episode Concluded" until Chapter 5, would he?

Unless he's using a guide it's not too likely that he will have gotten all of the Episodes Complete so I'm saying it'll be easier for him to start a new game and then keep track of things instead of starting a perfect run in Chapter Three and then discovering he missed something at the start.