Again, Sirius' design changed for some reason. I'm not bummed But I am confused.
* Siri, as a foal, didn't talk as formally as he does now. He only picked that up after hanging out with his Auntie Luna. She found the fact that a prince was talking like every pony else ridiculous and insisted on teaching him how to speak like royalty. That and she loved when he mixed the two up. It was adorable!
* As stated before, Discord taught Siri magic when he was a foal though he was shocked by how good he was with Chaos based magic. Siri has always been a fairly serious child so he didn't think he could actually do that kind of magic. Siri is very happy about impressing his teacher here but would later come to dislike this skill of his since he wanted to be like his mama, Celestia and not like Discord.
* While Sirius' and Toxic's friendship was short lived, they were super close. They'd always been seen together, though Toxic was rarely in his natural form when other ponies were around. Twilight was fairly distracted with her work and other adults mostly ignored Sirius but the few times they did pay him and his companion any mind, Toxic changed into Rigel Love.
Note: The design of Rigel Love is actually based on a webcomic called "Cosmic Funnies' by Jacqueline Moliner. It's a comic about the universe and explains cosmology and physics in a simplified and cute way. Check it out some time on either Tumblr or Tapastic.
*Celestia was the one to give birth to Siri and while her time with her son was short, she lived her baby. She had wanted to name him something simple but Twilight had already pulled out dozens of star maps and text books in search of a name, so Tia just let her have at it. It just meant she'd get to name their second child.