The long awaited Japan Animator Expo finale, THE ULTRAMAN: JACKAL VS ULTRAMAN, directed by Akitoshi Yokoyama has finally been released! You can watch it here for a limited time, and I highly recommend it!
That said, there are a TON of Easter Eggs throughout this short as fanservice to hardcore Ultra fans that not a lot of people may catch right away. Here are the big ones:
First off, the whole thing is derived from an epic Ultraman spin-off manga series, THE ULTRAMAN (Not to be confused with the anime co-production with Sunrise that featured Ultraman Joneus). The main arc of the manga that was adapted for the short, the Jackal arc, was translated and released by Viz in the 90s as ULTRAMAN CLASSIC: BATTLE OF THE ULTRA BROTHERS. It only lasted 5 issues and is long since out of print, but you can find them easily on eBay.
Melos should look/sound familiar. In addition to being adapted into a magazine photo comic and TV series, the character himself went on to inspire the looks of Ultraman Xenon in ULTRAMAN MAX, Ultraman Mebius, and the armor of Ultraman Zero featured in ULTRA GALAXY LEGENDS: THE MOVIE.
The opening battle is move-for-move lifted from the original Ultraman VS Zetton battle in ULTRAMAN, Episode 39: “Farewell, Ultraman”. Only, y’know…in space.
All the music is taken from a combination of Toru Fuyuki’s scores for RETURN OF ULTRAMAN and ULTRAMAN LEO, the latter of which being significant because of the source material, THE ULTRAMAN, being released after Leo’s run.
All the monsters Jackal turns into during the final battle are all Ultraman killers: Zetton (original Ultraman), Knuckle-seijin and Black King (Return of Ultraman), Ace Killer (Ultraman Ace), etc. The feathers surrounding Ultraman Taro’s death shot in the short are an allusion to Birdon, the monster who killed him in Episode 18 of his series. Birdon recently re-appeared in Episode 2 of ULTRAMAN X.
A bit of retcon application: The Land of Light featured in the final shot has its green glow that it picked up following the aesthetic upgrade in ULTRA GALAXY LEGENDS: THE MOVIE. Also, Blue Tribe Ultras featured EXTENSIVELY in the Jackal battle scenes. This is a huge deal because Blue Tribe warriors (ala Hikari) didn’t really become a thing in M78 canon until much later after the manga’s run.
Now edited and updated with more signs from other Ultraman/TsuPro series!
Again, this list is possibly incomplete as these are what I could find and and make out from images off the net. There’s probably more out there, because every Ultra has their own personal signature as far as I could understand. You can actually get one of these if you ask a suit actor in an Ultraman suit an autograph in some live event.