Final Fantasy XIII

Use the combination of the Jabberwocky&Bandersnatch and the single Wiadislaus in the final area of the Tesseracts just before/after the battle with Tiamat Eliminator to max out all core roles(or if you're really ambitious all current possible alternate roles too). Each of these fights found at the top of a long set of ramps(secret elevator on the opposites side in the corner) will net you 32000 CP. Just ride the elevator up, fight both sets, ride the elevator back down, run to the save, and repeat. Netting 64000 CP each trip 740000 will take you 11.5 trips. This should only take but 1-1.5 hours to complete for an already well established team.

This is the best place in the entire game to grind for CP quickly. I maxed out all character's core roles and gained the needed 740000 CP to max their specialties once the 10th Crystarium stage is unlocked after the final battle with Orphan and the credits are done. Keep in mind that 999999 CP is the max CP you can have at any time. So make two save files if you want to come back to this area to max existing alternate roles if you haven't already chosen to do so as you won't be able to return to this area post-credits. Doing this will aid in post-story gameplay and make maxing out those additional roles take much less time on Gran Pulse.

Since it takes the same amount of CP to max out any one character's specialty core role(740000), it is possible to earn all six of these achievements immediately after you reload the post credits save file.

Use the following choices to max each character's specialty role in the most efficient way possible. Light=RAV, Sazh=SYN, Snow=SEN, Hope=MED, Vanille=SAB, Fang=COM

You need lvl 10 Crystarium for this and enough Crystogen Points to get the Ravager role up to lvl 5. Stage 10 of Crystarium is only available after beating the final boss.