Ellen from 'The Witch's House'... just.... just play the game and you'll see.
I was kind of expecting more than just 9 fairly plain pictures of random video game villains/enemies with one to two sentences outlining who they are. I've never actually looked at one of the galleries before though so I guess this is probably the norm.
No no no, the Joker will only stab you in the back if it's funny.
For a real videogame monster, I present to you the Elder God.
He feeds off the souls of the dead and only becomes stronger as the world around him withers and dies.