Yet another story idea created through lack of sleep and way too much sugar...
Discord has been in Canterlot ever since the episode "Keep Calm and Flutter On" where he has made steady progress in turning over a new leaf and using his powers for good. However, Celestia still doesn't quite trust him, and so he's rarely ever able to really let loose with the Chaos. This eventually gets to Discord, and in a moment of intense boredom when Celestia just conveniently happens to be too busy to stop him from going too far, he decides to try something big, something he's never done before, something he doesn't even know if he CAN do.
Create sentient ponies from inanimate objects. We're not talking about a gravy boat that acts like a dog, we're talking about fully sentient and intelligent ponies, made from the first two objects his chaos summoned to him.
Thus, Smarty Pants and Tom became more than just an old doll and a large rock, and good old fashion Chaos ensues.
Of course, Celestia would probably not approve, so they certainly can't stay in Canterlot Castle with him. What he needs is to hide them for a few days while he tries to break the news to Celestia of his latest trick without getting himself turned back to stone at the end. Canterlot is a big town, surely they won't attract too much attention amongst all the other ponies, right?
Yeah, we all know things will likely spiral out of control, but that's probably exactly what Discord is hoping for, assuming he thinks of an explanation before the fun ends.