FFXIII-2 Fragment Location Guide | (#15) Ghast Fragment
Bresha Ruins (5AF) - Defeat the Cie'th
You'll find Chester beside a gate in the Bresha Ruins, looking for someone daring enough to take out a Cie'th. Seems like our group might be up to the task!
You'll find the Cie'th Ghast down in the second catacombs, after taking a hard left from where Chocolina is. Use Mog's Moogle Hunt ability to reveal the monster.
To fight the Ghast, use a combination of Ravagers to keep whittling his stagger bar down. Also have a Sentinel / Medic lineup ready for when the Ghast attacks, as it can hit pretty hard! Defeat this monster for Fragment of Time #15 - Ghast Fragment