This is a poem I wrote called Mary Sues Took Our Canon, and it's a parody of the children's book Aliens Took My Daughter (no copyright intended). I decided to leave it ambiguous as to which character was changed, other than it's a woman, because different people have different fandoms.

Mary Sues Took Our Canon

By Discofurby

It happened just this morning, something rather strange.

I read about this character and saw that she had changed.

The intelligent woman I once knew was gone without a trace.

I bet Mary Sues took our canon, and left one in her place.

Mary Sues took our canon, they thought we wouldn't know,

But what else could explain a lady full of uncanonical woe?

Or why this sensible woman would just kiss this rando's face?

Oh yes, Mary Sues took our canon and left one in her place.

She looked just like the character, but clearly she was not.

That character would not have the motivations this one's got.

Or try to kill her best friend just for breaking a special vase.

No doubt Mary Sues took our canon and left one in her place.

The author says, "Stop flaming me! She's not feeling her best!",

But she would never go around in that lacy dress,

Unless she'd been taken over by folk from outer space,

Or if Mary Sues had taken her and left one in her place.

We decided to take this case to the PPC.

They handle problems such as this very speedily.

They read the entire story, with lots of thought and grace.

"Clearly, Mary Sues took this canon and left one in her place."

Her angst was superhuman, her Aura of Smooth was endless,

She opened up a plot-hole and her mind was comprehend-less.

She was causing this fictional universe disgrace.

Why'd those Mary Sues take our canon and leave one in her place?

At last, two agents went on out and said, "You cannot stay!

You're busting up the canon. You must go away!"

They gathered all the charges and finally solved the case.

"Clearly, Mary Sues took our canon and left you in her place."

They attacked the Mary Sue, 'til finally she was dead,

And then, towards the plot hole, our agent friends did head.

They reached inside the plot hole and a miracle took place.

The character was back again, in her usual space.

So remember not to worry, if you should wake some day,

And find your favourite character has somehow gone away.

Just call up two agents from the PPC base,

Because we know that characters should not be replaced.