Dear Princess Celestia,
Um, Twilight doesn't know I'm writing this, so please don't tell her. I just wanted to know, however, um... Is it possible for a Dragon and a Pony to, well, have foals? And what they would be like?
Your Faithful student's number one Assistant,
Spike
Dear Spike,
Biologically, it is impossible for two vastly different species to breed. It would create an infertile foal, thus being painful for the parent and also acting as some sort of worm, if you will. It will use the mother's resources, and of course be growing scales that a normal pony would not be able to handle.
If you were to use Sleipnir's Mirror, it would turn out as a draconian pony. A pony, with scales. I am not sure if Cutie Marks would be possible, though. Basically, nothing drastic would be in appearance as far as relative odd goes. Of course, there would be very confused ponies.
So in conclusion, you will not be able to have foals with a pony. Our rising sciences may be able to biologically use your genetic code with another pony to create a technical pony-dragon foal. Seeing as you will be living for thousands of years, this is obviously going to happen.
Princess Celestia.