Goosebumps1995

Skipper Mathews:
Libby, you gotta be careful. The Mutant's in here! He could be anything. He could be the desk, or the floor, or the railing, or these pipes, or the ceiling!

Libby:
I know, I know, he's the Masked Mutant. He could be anything; he could even be me.

Skipper Mathews:
[in a wave of terror] Libby, that's not funny.

Libby:
There is no Libby - there never was.

Skipper Mathews:
Oh...

Libby:
[walks toward him, evilly] And now I must do something very bad to you, Skipper.

[Libby laughs maniacally revealing herself to be the Masked Mutant]

Skipper Mathews:
No, please! I'll just leave and take a bus home, and I won't tell anybody, honest!

The Masked Mutant:
[turns to himself, chuckles evilly] I can't let you leave! You belong here now!