So I've been binge watching Fairly Oddparents on youtube (the good seasons not the later ones), and Cosmo and Wanda's relationship every so often reminds me of how I write Discord and Celestia.

Discord definitely has more braincells than Cosmo does (bless the man he's doing his best), but I could see Discord saying a LOT of Cosmo's one-liners when he's fully reformed and has completely embraced his kooky old man side. Twilight is immensely glad at his progress, but his antics still bring her a little bit of stress from time to time, especially when Princess Celestia gets in on it. Darn you and your charms you old goat.

I also had originally considered having Luna be the one there, but then I remembered that Tara Strong voiced both Timmy Turner and Twilight, so the choice came extremely naturally after that.