My Little Pony and Friends/Nightmare Fuel

My Little Pony

 * In "The End of Flutter Valley", we're treated to a glimpse of what the valley would look like if the witches succeed. It's not pretty.
 * When the bees cover the Flutter Ponies is honey, Sting expresses concern that they may be drowned in it.
 * The opening to "Return to Tambelon", with the unicorns disappearing after winking out with no explanation as to why.
 * Erebus's plan in "Bright Lights" and the effects a lack of shadows has on the ponies.
 * Princess Porcina turning Ponyland and its inhabitants into glass, and her lackey's threat to do the same to Megan and the remaining heroes—and then shatter them.
 * In "The Magic Coins", Baby Lickety-Split, petulant over rain canceling the ponies' picnic, unknowingly steps on a magic coin as she wishes for it to never rain again. Cut to weeks later, where everything is drying up under the sun and the Baby Sea Ponies are dying of dehydration. And then a fire starts...

Moondreamers

 * The Night Mare, appropriately enough: an equine monster that the star-horse Andromeda turns into after falling into Monstrous Middle. If horses seem mundane to most people, the transformed Andromeda effectively illustrates how scary a horse might seem to hippophobiacs like the two-parter's human protagonist Timmy. (Although, revisiting the show as a grown up, the Night Mare is predictably less scary, though still a surprisingly good piece of creature design.)