Dinky Doo trilogy

Dinky Doo's Father Revealed is a fan fiction written by Roy G. Biv and can be found on Equestria Daily. It is one of the older fics out there, written with the intention of creating a Derpy Hooves story with a happy ending and explore the reason why pegasus pony Ditzy has a unicorn daughter.

Plot
The story opens with Dinky asking her mother who her father is. Ditzy, unable to speak with perfect coherence, instead provides her daughter with a box full of photographs and a scroll containing the story of Ditzy's life in a camp for ponies with special needs, where she was sent to undergo speech therapy. There, she met a mute unicorn named Bran Muffin, who had been secretly leaving her muffins in her room for weeks before she discovered him. The pair grow close as Bran teaches Ditzy the special sign language he uses to communicate, and eventually they fall in love and have Dinky. They go to live with Bran's adopted parents, the Cakes of Ponyville, for a time until the Farm requests that Bran return to his job as cook there until a replacement can be found. Bran never arrives at the Farm and is assumed lost.

Sequels
Two more stories were written to expand on the first. They chronicle a slightly older Dinky Doo's quest to discover the ultimate fate of her father.

Ditzy Doo
Ditzy falls under the "space cadet" level of the Derpy Scale in terms of her speech; her spoken sentences are peppered with random words that make little to no sense in context even after several re-reads. She is far more easy to understand when she writes or uses hoof-sign.

Bran Muffin
Rendered mute in a flood that killed his birth parents, he was adopted by his aunt and uncle Cake before going to the Farm to learn hoof-sign. He worked there as a cook while Ditzy was staying there for speech therapy, and sneaks muffins into her room to help put her at ease and make her smile. When the pair finally meet, he gladly offers to help Ditzy learn hoof-sign and the two fall in love.

Dinky Doo
Dinky is portrayed as a more grown-up and mature filly than she typically is in art and comedic Derpy/Dinky fics. She loves her mother dearly and, in the sequels, undertakes a quest to learn what happened to her father so that Ditzy can put her mind at ease on the subject.