In the Final Fantasy 13-2: you will need to locate all the Wild Artefacts during the Historia Crux to be able to unlock all the gates. The gates are activated by finding special artefact in hidden treasure chests using mog to locate them. Below you can find all the Final Fantasy 13-2 Wild Artefacts locations: Also if you are looking for the Final fantasy 13-2 Walkthrough for help go to the previous link in which you will find it helpull to complete the entire story mode.
Wild Artefacts Locations:
Sunleth Waterscape 300 AF: Use a Moogel throw during the ride along the anial trail
Bresha Ruins 005 AF: Use the Moodgle Hunt ability right after the tutorial
Oerba Village 200 AF: Use a Moogle throw on the side of the house near the big tree
Bresha Ruins 300 AF: Find the prased out NPC near the graveyard
Academia 400 AF: Can be found in an alley in the southeast of the map
Augusta Tower 200 AF: This one can be found on the 50th floor
Yaschas Massif 100 AF: You will need first to complete the Rubies of Grief quest, then solve the temporal rift
A Dying World 700 AF: You will need to fist complete the location of a dying world then return and chech the Farseers' Relic
Serendipity ??? AF: You need to purchase for 10,000 coins in whcih 7500 with the bargain hunter fragment skill.