Of Course the spirit of Christmas Present was changed to a pig to comply with the "no humans" policy. Pigs are the closest anatomical analog to humans!
Although, one would argue monkeys are closer to humans than pigs, but we haven't really seen any anthropomorphic primates in the show.
The alternate theme songs mention "trap Kris Kringle" among the Christmas activities. Considering that Kris Kringle, a.k.a. Santa Claus, is Scrooge's hated enemy, trying to capture him is probably among Scrooge's priorities (and indeed, Della sets up a net trap in the past, and the triplets set up a bear trap in the present, for exactly this purpose).
Related to this, setting up a beartrap for Santa makes sense if you remember that in this world, he is an anthropomorphic polar bear!
The Wendigo isn't shouting "Wendigo"; he's shouting "When'd he go?", hinting at his true identity as the Ghost of Christmas Past.
Earlier in the episode, Christmas Past kept telling that as time travelers, it's not where, but when they go - thus establishing that "When'd he go?" is a question that sounds natural from him.
The reason the Ghost of Christmas Past is angry at Scrooge is that he skipped last year's Christmas with the ghosts to spend time with his family on Mt. Neverrest. To him, up until that point, Scrooge was a person who was constantly living in the past, and constantly needed the Ghosts to relive his glory days. But then his family moved in and Scrooge wanted to let the past behind him and spend more time with them. And then he missed one Christmas with them, which signified to the Ghost of Christmas Past that he was not going to hang out with them anymore.
Scrooge seeing himself in the past in turn creates a time loop of confidence and assurances: Scrooge knows he will survive to be as old as he sees himself, and that nothing he will do until then can kill him or render him looking poor. He knows he will not die or fail because he met himself.
Preteen Donald being "some weird emo kid" seems like a 90's throwaway gag, until one remembers he was Born Unlucky and has a quacky voice that causes most characters not to understand him, take him seriously, or both. The endless frustration this would cause would of course make angry grunge music an attractive outlet for the emotions of a turbulent young teen.
Not only that, but his t-shirt and the "Nevermind" poster on his wall strongly suggest that he's a fan of his universe's equivalent to Nirvana. Their music was famous for being somewhat incomprehensible (Weird Al's parody of Smells Like Teen Spirit was all about this). It makes perfect sense that young Donald would idolize a musical act that became hugely famous despite being difficult to understand.
Donald mentions owning combat boots at one point. It's clearly a joke about his fame for not wearing them, but combat boots are a common staple of Emo Teen fashion. So of course Donald would have a pair of his own during his phase.
If you thought preteen Donald was incomprehensible, imagine what was his voice like when it broke upon hitting puberty and his reaction to it. No wonder he is so sour as an adult.
Speaking of his bad luck and quacky voice causing most people not to take him seriously, young Donald would probably want to distance himself from being seen as a joke by gravitating toward what he sees as a cool, serious, "soulful, devil-may-care loner type" image.
The title: Della is alive and working on a way to come home, so this may be the "last Christmas" she and her family spend apart.
Donald was surprisingly chill with Dewey essentially gallivanting across time and space alone. Except Dewey wasn't alone; Donald knew his younger self and Della would be with Dewey.
It makes sense Launchpad wouldn't know the words to "Twelve Days of Christmas"- besides Launchpad just being Launchpad, he wears a Hanukkah sweater in this episode, implying he's Jewish and thus his family probably didn't celebrate Christmas.
Launchpad is also Scrooge's chauffeur and pilot, and Scrooge puts on that he despises Christmas. This is the first year in a long time that Scrooge has not only allowed Christmas to be celebrated in his home, but joined the festivities as an active, willing participant. It's possible that Launchpad's been disallowed from celebrating Christmas by Scrooge as part of his employment for so long that he's long since forgotten the words to most of the songs.
Alternately, he's aware that his boss doesn't like Christmas and just doesn't wear a Christmas sweater when the day comes.
Launchpad's apparent Jewish heritage would also explain why he can't tell the difference between Christmas lights and landing lights. If he celebrated Hanukkah growing up instead of Christmas, he wouldn't have experienced the former while growing up. The fact that his employer would've never put them up himself, given Scrooge's apparent refusal to celebrate Christmas up until then, wouldn't have helped.
In the comic book continuity, the parents of Donald and Della (Scrooge's sister Hortense and her husband) didn't die until Donald and Della were adults. The fate of Hortense and her husband in this continuity hadn't previously been established, but "Last Christmas!" strongly implies Donald and Della were orphaned as kids and moved to live with Scrooge: the part set in their childhood clearly shows they're living permanently in Scrooge's mansion, and their parents are nowhere to be seen. This makes Della's disappearance as well as Donald and Scrooge's breakup even more tragic than it was before: Scrooge didn't just loose his niece and nephew, he lost his adoptive children. It also makes the comparison between Scrooge and Donald more obvious: they both adopted and raised the children of their dead, or presumably dead, sisters. This also further explains why Scrooge keeps telling Donald how proud he is of Donald being such a good and protective parent to Huey, Louie, and Dewey: Scrooge feels he failed Della by encouraging her reckless behavior and letting her get lost in space, so he thinks Donald is doing a better job as an adoptive parent than he ever did.
"The First Adventure!" thankfully puts the orphan theory to rest. Their parents are very much alive. In fact, it is revealed that the reason the siblings were even sent to Scrooge in the first place was because they lit a giant firecracker under their father's chair. After the first adventure, they decided to stick around to be his fellow adventurers.
Part of the reason Young Donald is so chatty is because he can still be understood. Adult Donald is forced to enunciate much more and is therefore comparatively direct and concise.
Obsession and desperation can turn people into Wendigos, monstrous creatures roaming the woods aimlessly. While the Ghost of Christmas Past got turned back in the end, who knows how many other people suffered a similar fate, without finding what they wanted...
Bankjob, Babyface, and Bugle are shown in the past working for Granpa Beagle. This begs the question, did these three pass away? Are they just old men now, or are three of the original series' Beagle Boys canonically dead?
As one commenter on Seaniccus review of the episode said, Donald at some point of his childhood had to confront the fact that his voice would be harder to understand as he grows older, and the grunge served as a way to express his anger and take advantage of his voice before the "change" happens.
said, Donald at some point of his childhood had to confront the fact that his voice would be harder to understand as he grows older, and the grunge served as a way to express his anger and take advantage of his voice before the "change" happens.