Skaroff the dragon? 
Basically, I just used my deepest base voice and a paper-towel tube and said “Mary, it’s the monster who lives under your bed! I hear you haven’t been eating your vegetables…”
Of course, now when she hears me do the voice she yells “Oooooo look at how plump I am! I bet I’m just delicious! I wonder if any monsters are going to try to catch me?” And then I have to chase her around the living room…
I never should have left my “Calvin and Hobbes” books lying around…
Thanks for all the ideas here. My daughter hasn´t started demanding made up stories yet. But I will often thrown in a small twist or variation to the normal stories as we read them. I switch voices and sometimes substitute the bears (when reading Goldilocks) for other animals.
Yeah, my son’s only 5 months, but I’ve been reading to him since he was born. these ideas are going to come in VERY handy. Warped at a young age, how nice!
Goldilocks Now! (Apocalypse Now)
Goldilocks, whose mission is “Terminate with extreme prejudice”, receives orders to seek out a renegade military outpost led by a mysterious Colonel Kurtz during the Vietnam War.
Goldilocks X (Jason X)
Goldilocks awakens from her long slumber to slaughter the crew of a space ship.
Goldilocks and the Holy Grail (Monty Python and the Holy Grail)
Goldilocks and her Knight Bears are given a quest by God to find the Holy Grail.
Goldilocks and the Meaning of Life (Monty Python and the Meaning of Life)
…
…So…yeah. 
Try this one: Goldilocks meets Shrek the big, smelly, ugly, green ogre (good place to reinforce that looks aren’t everything) and fights with Princess Fiona over him. However, in the end, the princess pulls rank and wins (exposure to how the real world works- the person with the most authority and power wins), and poor goldilocks is rejected. She then meets Lord Farquaad and lies about being a princess, so he marries her. The bears, angry at being previously robbed of their porridge, kidnap her and carry her off to their house, where they make her sit and watch them eat porridge everyday while she isn’t allowed any. Finally, the donkey enlists the help of his girlfriend, the dragon, to rescue poor Goldilocks, and they carry her back to Lord Farquaad. There, he finds out about her humble origins and then forces her to endure a miserable life locked in the castle tower until he can divorce her and marry Cinderella. (For a more child-suitable ending, Lord Farquaat can discover her humble origins but love her anyway)
I guess you kind of had to see Shrek to understand that, but I’m assuming that your daughter probably did. Hope she enjoys this! 
monica –
MilliCal has seen Shrek many times over, and has subjected her grandparents to it twice this past weekend. Gid knows what they made of it. Certainly MilliCal doesn’t realize how iconoclastic it is. She’d certainly recognize the story as you tell it, but I’m not sure how she’d like the liberties taken with the story, which is now canonical to her. But I might try it.
Additional warpage:
Last night MilliCal stumbled out of bed for the umpteenth time (as part of her ongoing sleep-avoidance program) and saw a commercial for South Park on Comedy Central. She immediately perked up.
“Mommy, Daddy, Can I watch that one night when I don’t have school the next day?”
“No,” we chorused.
“Why not?”
And so we patiently explained that it was not a Children’s cartoon.
“But I saw it on Arthur,” she riposted.
It was true. The animators on the PBS series Arthur, probablt to amuse themselves and parents, had animated part of one episode in the torn-out-paper style of South Park. I am amazed that MilliCal a.) remembered this; b.) could come up with a way to use this in her argument that she should watch it; and c.) already headed off our argument that it was on Too Late at Night with the proviso that she wanted to see it on a night when she didn’t have to go to bed early. I have to keep reminding myself that her aunt is a lawyer. (MilliCal is still not 5!)
Goldilocks goes Where the Wild Things Are - "And the Wild Things roared their terrible roars. ‘We’ll eat you up we love you so!’ And they did. "
StG
Goldilocks had been in so many stories that she was really famous. In fact, she was so famous that she was recognized everywhere. No one would leave her alone; everywhere she went it was “Look, golden curls! It must be Goldilocks!” Tired of never being left alone, Goldilocks decides to try dying her hair. First, she tried being a redhead. However, after numerous run-ins with little leprechans convinced she was Irish, Goldilocks decided to dye her hair purple. However, after being approached by too many scary punk-rockers, she decided to go brunette. However, upon encountering the bears, they didn’t recognize her. Goldilocks decided that being with her friends was important enough to go back to normal (golden-blonde), and now she just looks at the paparrazzi’s cameras with pride. Moral of the story: Its important to be yourself.
Our daughter MilliCal is still at it. She demanded “Goldilocks and the Three Stooges” this week, complete with the Clam in the Porridge, the Murphy Bed, and the Duck that Drops Down with the Secret Word she confuses the Three Stooges with the Marx Brothers).
As an added wrinkle, she keeps wanting me to tell her the story of The Gingerbread Terminator.
[Arnold Schwarzenegger] Ha! Ha! Ha! You Can’t Stop ME! I’m the Gingerbread Terminator![/Arnold Schwartzenegger]
("YOU started this!’ accused Pepper Mill, “You can explain it at Pre School!”)
Well, as a baker IRL I can supply you with a solution that will stop an unstoppable killing machine made of gingerbread. Moisture. That’s it. High humidity, water, whatever. So when Linda Hamiltom and son are in jeopardy, all she needs to do is turn a hose on the creature.
CalMeacham, my daughter demands something similar - stories involving her toys and anything else in the room. Sometimes I make up an original story, or make one up where Al Jr has to provide some of the words (one day Doggie and Teddy went to the … [insert park, woods, zoo, etc). Sometimes, however, we do something similar to you, and transport her toys into familiar stories - ‘The three little dolphins and the big bad shark,’ for example (with houses of seaweed, driftwood and stones).
I like the idea of the Gingerbread Terminator - may steal that one, if you don’t mind.