The year was 1997.  Juan Valdez was leisurely leading his donkey through a barren part of New Mexico, searching for the perfect coffee beans to hand pick.  He didn't know, however, that military scientists were conducting nuclear experiments in that very field!
There was an explosion and Juan was disintegrated immediately.  But his donkey survived!  Some how, the baskets of coffee beans, the riding blanket, and its own stubbornness, saved the ignorant beast!
Now the donkey wanders the country, in search of its lost master.... yet it hides a terrible secret.

Present day:

Billy kicked a stone into the canyon in frustration.  His parents wouldn't let him try and slide down the sheer cliff face on his bottom.  Oh it's the Grand Canyon!  Whoop de doo, he thought.  It's no fun if he can't play in it.
"Maybe if we hire one of those touring mules?" suggested his Mom.
"It's too expensive," replied his Dad.  "We'll just take some pictures from this lookout."
Billy sat his butt on the ground and plopped his chin into his hands in boredom.  If only there had been a slide, or a target to pelt rocks at, or SOMETHING for a kid to do.
Just then he noticed a lone figure standing in the distance.  He strained to make out the shape through the rippling heat.  With his parents preoccupied with snapping photos, Billy got up and walked towards the figure unnoticed.  As he drew closer he realised it was a donkey!  A donkey!  Hey!  He could ride that down the cliff.  His Mom said so.
Billy grabbed the reins of Yuan's Donkey and pulled.  The donkey snorted in disgust but did not move.  So Billy yanked harder.  The donkey merely shook its head.  "Come on you stupid a**!" cursed Billy with a mighty tug.  Instead of complying, the donkey lowered its nose to the ground and glared at Billy with more intensity than his grade school teacher, Mr. Spanks.  Even more disturbing, the donkey's eyes turned green, and he began to shake violently.
Billy dropped the reins and backed away slowly.  When the donkey started to bray in guttural tones that would scare a lion, Billy turned and ran.  Suddenly the donkey was there, madly blocking Billy's escape.  It paced with a dangerous ferocity, eyes always locked on the boy.  Its dull grey fur bristled and turned green as its muscles rippled and grew.  In seconds the beast had doubled in size.
Billy lost control of his bladder with the fear.  The sight of his trembling weakness made the donkey bray with laughter.  So much so, it quickly returned to normal and then sauntered off.
Billy ran back to his parents once it was safe to do so.  "Aw Billy!  What have you done?" his father said, regarding the soaked pants.
"There was this donkey!  He turned all green and muscley -"
"Enough of your stories!" interrupted his Mom.  "You'll have to stay in those wet pants now for the rest of the day, until we get back to the hotel."   In the distance, Billy could hear the laughing bray of the donkey.  He frowned and returned, much less comfortably, to his seated position and scowled.

"You'll rue the day you peed your pants," his father said walking up to him and wagging a finger.  "I'm not running the air conditioning in the car.  I hope that will smarten you up.  The reek will make you want to puke.  And if you do puke, we’re still not stopping.  This is will be your rite of passage, at least for this month.”  His father walked away still wagging his finger.
Billy didn’t know what he hated worst, that he wanted to puke or that his father knew he wanted to puke.  Billy stood up and leaned over the side of the canyon.  The braying laughter continued unabated.  He closed his eyes and thought of Lawrence of Arabia and promptly projectile vomited into the canyon.  He opened his eyes to watch the soaring vomit plunge.  (Later he would create his own unique painting style.  He would ingest paint and then projectile vomit it back on the canvas.  Art-lovers everywhere would proclaim him the new Pollock... by calling him the Puking Painter).
Suddenly the braying stopped all of sudden.  Billy was scared, his sphincter tightened and then released the previous day’s chilli.
“You’ll have to sit in that too,” His father yelled from 60 feet away.  Everyone heard the sickening echo of a loose bowel movement.
Even more suddenly than before the sound of galloping hooves increasing in size came closer and closer.  Billy could smell the coming doom.  He turned around and saw…

...John Tesh.

Billy hated John Tesh every since he left Entertainment TOnight.  And Billy certainly didn't like John Tesh's syndicated radio show.  To prove he didn't like John Tesh, Billy puked again, this time at John Tesh.

John Tesh shook his head in rage.  He gently took off his shirt and exposed his upper torso showing the scars of many a night in a viet kong prison camp.  He had never served in Vietnam, but went there to experience torture first hand.  "You remind me of Mary Hart, boy... And I hates Mary Hart!"

Billy quivered with fear... he turned to run...

...but ran into Mary Hart... She too took off her top and showed the scars of vietnamese torture.  She had done the same thing as John Tesh saying "Anything choir boy can do I can do better."  She was right, she endured, voluntarily, more torture than John Tesh did.  How did she know she had endured more?  Easy, she went to the Vietnamese Advanced School of Torture and Accounting... same place John Tesh did.  She stomped her feet and snared like a blue jay, "I hates John Tesh."  She smacked her lips.

Billy, unsure of where to run, just stood there gaping at both John Tesh and Mary Hart, Giants of entertainment news.  He marveled at how nice their hair was.  Suddenly, the green donkey leapt from nowhere to land on another side of billy.  He found himself in the middle of a deadly three way show down.  His next move could well be his last...

... and it was.  Billy soiled himself and spun like a top.  All those years at ballerina school finally came in handy.  Unclean matter flew at the trio surrounding Billy.

"My hair!" screamed both John Tesh and Mary Hart with enough force to cancel each other's sound waves.  The air trembled but nothing was heard.  The entertainment hosts clawed at their faces in horror and bolted from the scene.

The Incredible Donkey, however, was used to such conditions.  It made him feel at home.  Slowly he changed back into a normal donkey, covered in filth, and brayed with merriment.  As Billy finally collapsed from his dizzying spin, the donkey happily trampled the poor lad to death...  for trampling little boys was something else he enjoyed doing at home.

When Billy stopped twitching, the donkey began to walk solemnly down the road to sad piano music.  His play time ended, the donkey looked forward to a long, uneventful walk to yet another random location in his never ending search for his master.

As the donkey faded from view, the pianist packed up his portable keyboard and prepared for his journey, ever linked to the monstrous killer he trailed.  The sights he'd witnessed over the years, providing incidental music, scarred his soul.  Yet he continued, for he must.  This was his curse.

A few short days later the Donkey found itself in a dark alley in Las Vegas.  It was dark to the donkey because its eyes were closed.  He opened them and saw a sight he never thought he’d see in his entire life.  It was a disgusting trash dumpster filled to the brim with half eaten condoms and used food… then the donkey remembered it was dyslexic.

With a gleeful snort he clippity-clopped to investigate the food for he did not eat on his long journey from the grand canyon.  There was an annoying hum in his ear and he brought is rear hoof to his head to scratch just like a flea bitten dog with fleas… and piles.  The humming intensified and changed pitch as he feverishly scrubbed the fur of his ear.

The pianist’s keyboard had run out of batteries and he was forced to hum the ‘Alley soundtrack’ by improvisation.  The donkey shrugged as only a donkey could, with all four limbs and pranced into the dumpster.  A scream erupted from the dumpster, which startled the donkey… he quivered and snarled as the change began…

... except it wasn't Donkey's change...  the dumpster slowly changed, with clanks and gears, into a giant robot.  "Dumbest Transdeformer ever," mumbled the pianist between verses of humming.

The Donkey, having never seen a Dumpster-bot, was rooted in place with fear, trembling at this former food basin become misshapen anthropod.

"I am Dumpstar," greeted the robot.  "I am searching for the All-Spark Matrix Cube-i-tron by remaining in one place.  Some day, statistically, someone will dispose of the Cube, and I will be waiting."

Donkey was suddenly enraged.  He hated to the core all things with names that started with "D", especially lazy dumb a** names like "Dumpstar".  Even more, he hated to the core of his core anyone who used statistics to justify anything.

Muscles bulged abruptly from Donkey's quickly greening fur.  His ears folded back in rage as he faced the robot.  The Pianist switched from humming to choir "Aaaahs" in a rising crescendo.  Before Dumpstar could decide if this was an aggressive or submissive posture, Donkey leapt into Dumpstar's midsection, head first.  The impact threw Dumpstar down the length of the alley.  Slowly the robot regained his feet, looked around, and screamed.  He had moved from his position.  Statistically he'd have to start waiting all over again from where he was now.

Donkey, recognizing the scream of statistical analysis, went berserk.  In his frothy rage he....

... stomped his hoof hard enough to crack the earth.  A new fault line formed under Dumpstar, and tectonic shift was enough to open into a gap precisely the width of a garbage bin.  As the robot plummeted into the chasm, it sighed with resignation.  Now Dumpstar would have to wait eons before archeologists discovered him, and resumed using him as a trash receptacle.  The sigh, of course, reverbrated off the pit's walls and started an avalanche.  Rocky earth collapsed inwards and buried Dumpstar.

It was, in Donkey's opinion, the minimum amount of punishment for anyone using statistics.  The only thing Donkey hated more than statistics was stories that took nearly four years to tell.

As the pianist hummed a sad ballad, Donkey reverted to normal size.  He turned, kicked extra dirt into the pit like a dog after a poop, and then clip-clopped off into the sunset.