Walkthrough: After finishing your Trial with Acerola, you can actually stick back or return again to the Abandoned Thrifty MegaMart to hunt for all those strong Ghost Type Pokemon. There are no trainers or items found here; only Wild Pokemon can be discovered.
Wild Pokemon:
Walking (Levels 29-32): Golbat(40%), Haunter(40%), Klefki(15%), Mimikyu(5%)
SOS Pokemon #1 (Levels 29-32): Golbat, Gengar, Klefki, Mimikyu
SOS Pokemon #2 (Levels 29-32): Golbat, Haunter, Klefki, Mimikyu