Ensemble Dark Horse: Raritoot (Rarity as a magical talking tuba) from "Applejack and the Beanstalk" left a big impression on fans, to the point where Raechel Anderson, who voiced her in that episode posted a set of bloopers from her recording of the lines on her channel. Even more impressive, it was the actress' first time voicing Rarity in general. She even made a cameo appearance in "Discord Tales".
Fridge Logic: As Pinkie The Giant points out, as a giant she could have easily been down the beanstalk before the heroes even had time to find the ax, so she just waits patiently for them up their until it time for them to cut the beanstalk down.
In "Egghead and the Beast," Twilight has to solve a riddle where the answer ends up being friendship. Another riddle like that would end up appearing in the MLP holiday special Best Gift Ever.
"Egghead and the Beast" also features Chrysalis teaming up with Tirek and King Sombra, where Pinkie points out it is unlikely the villains would get along with each other. In season 9, the three villains are recruited to work with each other. While Sombra refuses to work with the other two villains, on the other hand Chrysalis and Tirek eventually learnt to work with each other.
In "Raripunzel," when Silver Quill (the narrator of this particular story) is shocked to hear that Pinkie has never seen a hippogriff before, she replies by saying there aren't any in Ponyville. Not only would she actually meet hippogriffs later down the line, but they look far different from how Silver Quill designed his OC.
Applejack being a fourth wall breaking character in this series is just like how she is characterized in the spin-off series My Little Pony: Pony Life.
One-Scene Wonder: Spike in his two brief non-speaking appearances in The Three Little Pigs and The Big Bad Rariwolf as Rariwolf's little wolf assistant and in Shaladdin when Pinkie briefly turns Appol into a dragon.
In-Universe, this is pretty much done on purpose, as various characters are often put into unfitting roles because of Rule of Funny, like making Applejack the fairy godmother, which even Applejack thinks was a weird decision. Taken up to eleven in Slumber Jack when Pinkie decides she wants to play the villain and switches roles with Chrysalis. From then on the story treats Chrysalis as though she’s an earth pony with Pinkie’s characteristics. Until Applejack gets so fed up with Pinkie's shenanigans that Pinkie switches back before Applejack can deal the killing blow to Dragon Pinkie.
For the voice actors themselves, during the auditions for "Discord Tales 2," when the fans heard that Sunset Shimmer would be one of the characters in the episode, many of them stated their hope for (at the time) fan favorite VA Wubcake to voice her, which only strengthened when she announced that she would be auditioning. However, in the end, the role of Sunset was given to Kenzie VA. Many were shocked by this decision, saying that they couldn't imagine how any fan VA could get the role of Sunset over Wubcake. However, Wubcake herself voiced her support for Kenzie, and once people listened to her audition lines, they admitted that she could do a decent Sunset impression. The fact that Wubcake had already had roles in previous Pinkie Tales episodes (Applejack in "Little Red Riding Bloom," Aria in "The Little Mermare," and Zecora in "Raripunzel") might have meant that Magpiepony wanted to give someone new a chance (Kenzie had auditioned for roles ever since the "Shaladdin" episode but never got one until this point). Given later revelations about Wubcake's behavior, Magpie may have dodged a bullet that particular time.
. Even more impressive, it was the actress' first time voicing Rarity in general. She even made a cameo appearance in "Discord Tales".