Cosplay As Jeff The Killer:
Get a mask and spray paint the black around the eye circle. Then paint a smile, similar or exactly like his. Make sure it looks scary, then go up to children, tap them, and when they turn around say "Go To Sleeep" until someone tells the staff to kick you out.
Cosplay As Slendy:
Get a suit and then buy a white mask with no eyes and go behind random people and follow them around the store until they kick you out.