Maud: “ Remeber Rocky, owning a pet such as Cliff here is a big responsibility. You must give them the attention they need and make sure they get plenty of fresh air, as well as let them socialize with other rocks now and then. Do you think you can handle that?”
 
Rocky: “ I…I think so.”
 
Maud: “ Good. Don’t ever forget, rocks aren’t just pieces of granite and limestone. They are our friends. They listen to you and are there for you. Unlike…some ponies, rocks don’t judge you for who you are. “
 
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May I introduce to you Pinkie pie’s third child and only son: Rocky, and his pet rock, Cliff.
 
 
Growing up, Rocky didn’t have anyone in his family that he could relate to, except Maud. She could relate to her nephew’s trouble making friends and his tendency to be obsessive over whatever it was that he was passionate about, along with a few other oddities. So it was only natural that Rocky would reach out to his Aunt and form a bond with her that, perhaps, is even stronger than that with his own parents.
 
Rocky had no one he could really call a friend during his childhood, and when he talked to Maud about this, she suggested getting a pet. A rock pet. Rocky wasn’t really fond of stones and such, but the idea of having a companion he could talk to that wasn’t himself was appealing. So he ended up adopting a little Sandstone chunk of a rock and name it Clifford, Cliff for short.
 
Even though Rocky eventually found some friends as he got older, he still has Cliff to this day and is very attached to his quiet little friend.
 

 
also, it’s so hard to find a good background these days. :/