Acting for Two: The voice actors for the three Buddyroids all get to have on-camera roles (while still playing the Buddyroids as well). Cheeda Nick's actor plays a man who gets lost, Gorisaki Banana's actor plays a school teacher, and Usada Lettuce's actor plays Atsushi Doumyouji/Green Hippopotamus!
Actor Allusion: The extra roles of the buddyroid voice actors each have something to do with their corresponding buddyroid. Nick's actor getting lost is a nod to Nick's horrible sense of direction, Gorisaki's actor comments on the copious heating pads that Dobutsu!Ryuuji wears (Gorisaki always worried about Ryuuji overheating), and Dobutsu!Yoko is immediately attracted to Usada's actor.
Chekhov's Gun: The Dobutsu Verse mecha are shown to only be able to use its full power with six Busters in the cockpit (which is why Black Puma needs to join the team after Atsushi dies). When all nine Busters pilot it in the Final Battle with Azazel, it's capable of defeating Azazel when neither it nor Go-Buster King (it's alternate counterpart) could so much as phase him with the teams piloting it solo.
Continuity Nod: The "Laboroid" versions of the Buddyroids in the Dobutsu timeline refer back to Go-Busters vs. Gokaiger's factory reset versions of them.
Cross Counter: Hiromu's and Ryuuji's argument in episode 5 is capped off by this.
Curbstomp Battle: Both versions of the Go-Busters' fights with Azazel end this way. They return the favor later on.
For Want of a Nail: Shows what would have happened if the Messiah incident had never occurred.
In Spite of a Nail: Even in a world without that incident, a group of enemies cause a different version of the Go-Busters to be formed, and the same thing happens on the New Year that happened in the main timeline.
Funny Background Event: J pulls off tons of these whenever he's not the focus of the shot, wandering around and picking up random things. For example, when the other members of the Dobutsu Sentai huddle together during a harrowing mecha battle, J quietly joins them while cradling one of the cockpit's decorative plastic flamingos.
Interquel: The story is set between episodes 44 and 45 (after Escape and the revived Messiah are killed, but before Enter reappears).
In a Single Bound: Parodied, naturally. In many series, rangers often use this technique to board their mecha, but Dobutsu!Kuroki and Gold Beetle learn the hard way that it's not terribly easy to do, especially when you're older. At different times they attempt to pull this off, only to leap barely a foot into the air and strain their backs.
Instant Expert: Hiromu, Ryuji, and Yoko of the Tokumei Sentai had been training since their childhoods to prepare for both fighting as Busters and piloting the Buster Machines. Hiromu, Ryuji, and Yoko of the Dobutsu Sentai, on the other hand, are recruited by Kuroki with no prior training and are then sent to fight monsters and pilot their mech that same day. They win.
In the Name of the Moon: While the Tokumei Sentai had a pretty simple roll call, the The Doubutsu Sentai's is more elaborate:
Lighter and Softer: The Dobutsu Sentai universe, as compared to the Tokumei Sentai universe.
Make My Monster Grow: Unlike the regular universe, Mechalius uses this trope to start its giant fights, so rather than fighting separate Megazords, the Dobutsu Sentai just fight giant versions of the monster they just fought.
Azazel starts out at giant size then shrinks down to fight the Go-Busters when he's defeated their mecha. After the combined might of both sets of Go-Busters destroys him in the first onfoot fight, he returns to giant size for one last fight.
Mayan Doomsday: Gorisaki mentions this at the start of the movie. It's heavily implied that Azazel is the bringer of said doomsday.
Motion Capture Mecha: The Dobutsu Sentai's mechs. Their control system is the ambiguous kind that responds to the Busters' body movements, but also appears to accept input from a "console" made of what looks like a small tree trunk. This is, of course, in stark contrast to the Tokumei Sentai's mechs, which have much more realistic (or rather, plausibly complicated)-looking cockpits and controls. Naturally when the two teams team up in the end, the Tokumei Go-Busters are understandably confused until the Dobutsu Sentai ones show them how it works.
Oh Crap: Azazel has one when Go-Buster Perfect Animal (the Dobutsu Sentai's version of Go-Buster King) powered up by having all nine Go-Busters in the cockpit at once No Sells his attack. He has another one when it's preparing the Go-Buster Miracle Flash that destroys him.
Outside-Context Villain: Azazel is not affiliated with the Vaglass, and his title of "Great Demon Lord" indicates that he's a supernatural entity, something that the Go-busters never faced at any other point in their series.
Palette Swap: The Green Hippopotamus and Black Puma suits are repaints of Blue Gorilla's and Red Cheetah's suits respectively.
Romantic Plot Tumorinvoked: Implied to be the case in the Dobutsu Sentai Go-busters "series" as part of the parody. Episode 15 kicks off a Love Triangle, and it remains a plot point all the way until Episode 37 (The only episode shown inbetween those two (28) even has Red Cheetah and Pink Cat discussing it).
Self-Parody: Showa-era Super Sentai tropes are exaggerated and lampshaded to such a tremendous degree that even the Akibarangers would be proud. Dobutsu-Hiromu even looks a little like Nobuo in that red jacket.
In the final battle with Azazel, the Dobutsu Sentai summon their Humongous Mecha by saying its name, followed by "Kourin!"* (Advent). This is the same incantation used by the Goseigers during their mecha summonings/combinations.
The Dobutsu Sentai's "Go-Buster Ball" attack is a direct reference to the "Goranger Storm" attack from Himitsu Sentai Goranger, and is executed in the exact same way.
This isn't the first time that a "Returns" special has featured an animal-themed alternate version of a Sentai team- it happened to the Shinkengers as well in their special (specifically, Ryuunosuke's illusion).
Super Multi-Purpose Room: The entrance to Kuroki's secret base is a staff room in the school that becomes an elevator leading to the base.
"Super Sentai" Stance: While the regular Go-Busters had more subdued posing sequences, The Dobutsu Sentai take it the whole nine yards. Funnily enough, J's posing is perfectly in sync with the rest of the Dobutsu Sentai despite never having done it before, leaving Nick wondering how he even knows what to do.
Take That: Many people believe this movie was created in response to the people who criticized Go-Busters for being different than the standard Super Sentai series. Strangely, despite this, the Dobutsu Sentai Gobusters are still treated somewhat respectfully in the Final Battle, kicking just as much tail as their more serious counterparts.
Tempting Fate: Gorisaki notes that a lot of crazy stuff had happened that year, and he hopes that they can see the year off without any more trouble. Nick immediately yells at him to not jinx it.