Teen Wolf, Season 5

Deaton:
Hold on-- Scott might have something. Mason's twin wasn't entirely gone. That's what made him a genetic chimera. The DNA was still there. Metaphorically speaking, the DNA of Mason could still be inside Sebastien as well.

Stiles:
How?

Deaton:
Life is energy. Energy doesn't just disappear. The Dread Doctors may have found a way to break the rules of the supernatural, but there are some rules that simply won't break.

Liam:
So, Mason can't just be gone?

Deaton:
Somewhere in Sebastien, he has to still exist in some form. A spark of energy, a flicker of memory...

Stiles:
Hang on... Liam, you said Mason said something right before he turned.

Liam:
He said, "That's not my name."

Scott:
He finally remembered his name. Damnatio memoriae.

Deaton:
That's what they wanted. They wanted Sebastien to remember his name. Scott, do you know the myth of what happens when you call a werewolf by its given name?

Scott:
[shocked] It turns back to human...

Liam:
What does that mean? Someone can just walk up to the Beast, yell Mason's name, and turn him back?

Stiles:
Not someone... Lydia.