We learn in this episode that Launchpad writes Self-Insert Fic about Darkwing Duck. This means that the actual Darkwing Duck episodes, which feature Launchpad as Darkwing's sidekick, may exist in the DuckTales universe as Launchpad's self-insert versions of his favorite episodes.
Word of God says that a Darkwing Duck with no Gosalyn is not really Darkwing Duck. We see no signs of her in Starling's show, and since she's getting introduced in Season 3 we can be sure the Darkwing on television had no children. Meaning that if any episodes of the OG show could have been this Launchpad's rewrites they'd need to be ones that didn't include Gosalyn or Negaduck.
"The Scarlet Pimperbill" looking so similar to Darkwing is understandable since Pimperbill is a direct reference to The Scarlet Pimpernel, an early example of The Cowl and inspiration for works like Zorro and Batman. As Darkwing himself is a parody of such heroes, it makes sense that, in universe, he was at least partially inspired by The Scarlet Pimperbill.
Lena's violently possessive response toward the idea of being replaced by another female friend makes a lot of sense given how for most of her existence Magica was such an influence on her (and indeed Lena was created from her). For Magica, if something was valuable then it was to be possessed and controlled, and not given up or compromised. As much as Lena hates Magica and everything she stands for, it makes sense that she still took on some of Magica's traits. Likewise, her own experiences as a manipulator make her prone to see it in others.
It also makes sense for Lena to be overprotective of Webby. She's not only the only friend Lena ever had, but is also the very first person to show Lena what love and a true family are. So, of course, Lena's not willing to let anything happen to Webby.
This episode got kicked fairly far Out of Order (originally between "What Ever Happened To Della Duck?!" and "Treasure of the Found Lamp!"). But because of this it ends up fitting nicely with "Raiders of the Doomsday Vault!" as a companion episode, like they took place at about the same time since the casts don't overlap.
Good news is Lena's back. But...Magica is still around and may resurface. Sooner or later, Magica will find out one of the three girls has her amulet, and it would be a bad idea if any of them were caught with the amulet on them...
