The ponies head out in force to celebrate the first day of fall. Baby Lickety Split, Baby Shady and Baby Tiddley Winks head further from the house than the rest, and Baby Tiddley Winks falls into a river. The current proves too strong for the others to dive in and rescue her, but she's saved when a gigantic dog comes out of the woods and pulls her out. Naming the dog Dinah, short for "dinosaur" on account of her size, the baby ponies bring her home and cajole the others into letting the dog stay.
As fall and winter pass, Dinah's stay at Paradise Estate proves rocky. Her size, playfulness and puppy-like clumsiness do not mix well, as she constantly knocks things over simply by walking by them, and her supersized appetite also proves difficult to deal with. Despite this, the ponies find themselves growing fond of her, even Lickety Split, despite the irritated front she puts up around others.
When spring arrives, the ponies find two surprises. The first is that Dinah hit a growth spurt and is now even bigger. The second is a trio of giant dogs that comes out of the woods and calls to Dinah. Realizing that this must be Dinah's family, the ponies reluctantly let her go with them back into the wild, despite knowing that they'll miss her — even Lickety Split.
This episode contains examples of:
- Amusing Injuries: What Dinah's antics inevitably lead to throughout the episode, including a sofa crashing on Magic Star's head at one point.
- Breather Episode: "Pony Puppy" is a light-hearted, slice-of-life story about ponies adopting a dog in between stories about all of Ponyland being turned to glass and an evil wizard stealing everyone's shadow-slash-souls.
- Canis Major: Dinah is, at the minimum, the size of a rhinoceros, and she's still only a puppy.
- Merchandise-Driven: Truly can be seen wearing the Flashprance
outfit in this episode, which was part of the year three pony wear series. - Pet Baby Wild Animal: Dinah is, outside of having the appearance of a domestic dog, a fairly straight example. The ponies find her wandering the woods after being separated from her pack, and the episode ends with her being returned to the wild to be with her kind.
- Pet the Dog: Almost literally. Lickety Split is very vocal about her dislike of Dinah, but feeds her treats when nobody is looking and cries when she has to be released.
- Your Size May Vary: Even before her growth spurt, Dinah shifts between "just" around the size of a rhino to being much taller than trees.
