I choose to believe that the dog with a weird marking on its back that appears in a Painwheel flashback is Samson, possessing a dog for a host, as he is eyeing up his next victim (Filia).
Just based on Filia's facial expression in the couple of flashbacks we see of her, I choose to believe that she was a major bitch before Samson got to her. Here's the backstory I made up for Filia.
Lab Zero told Valentine to kidnap a schoolgirl to use as a test subject. Valentine targeted Filia and cornered her, but Filia begged Valentine to spare her, saying that she was a member of the Medicis and that there would be a giant commotion if she was kidnapped. Filia said that she could provide a much better schoolgirl to kidnap. Valentine wanted to avoid the commotion of kidnapping someone important, so she decided to trust Filia.
Filia hated Carol, so she decided to trick Carol into following her to a location where she was kidnapped by Valentine. Valentine whisked Carol off to Lab Zero, and she was turned into Painwheel.
On her way home, Filia complimented herself on her two accomplishments. Not only had she avoided being kidnapped, she had also gotten rid of her least favorite classmate at the same time. While she was laughing happily about her achievements, she attracted the attention of a certain dog. She likes dogs (this is real, it's in her official bio
) so she stopped to pet the doggy, and then...Samson struck.
For nourishment, he ate her memories, and then pretended her didn't know why she was suddenly an amnesiac, and feigned sympathy for her to make sure she would be a compliant host.
At least, all of that is what makes the most sense to me!