As it is tradition in all original Dragon Ball movies, Dragon Ball Movie 3 Mystical Adventure is basically a retelling of what happened up to that point slidly altered. Chaotzu is an emperor with Master Shen and Tenshinhan being his underlings. Bora, Upa, Tao Pai Pai, Nam, General Blue and Arale appear in this movie but with lesser roles compared to their anime counterpart and some references are made to the main story but without the same impact. In fact, it might be the weakest of all 4 purely Dragon Ball movies simply because the scenes that end up being weak homages could never carry the same impact as most of them were build up for several episodes or even story arcs. Examples such as how General Blue dies as we was set up as a big threat causing trouble to the main characters in the main story, while here he doesn't have the same set up so his death doesn't give the same feel.

Meaning it is nothing but a 46 minute movie that feels like an extended episode.
Even the way Goku surpassed Tao Pai Pai felt like an asspull where he somehow ended up at the top of the Quin Tower and received a minor advice from God of Martial Arts Korin, instead of training or drinking the holy water. Compare that to how Goku worked his ass off to get to the top and received training disguised as a power up (instead the other way around like in modern Dragon Ball).

But what about elements exclusive to the film? There is an inner conflict in the nation where the story mainly takes place. Tenshinhan is conflicted what side he should take in the conflict: Loyalty to his teacher or his Emperor. Sadly this element like many others aren't taken full advantage off. Like we don't know about Tenshinhan's past events with his teacher. Only a small hint of his relationship with his Emperor.

The story has 2 subplots. The gathering of the Dragon Balls and the Tournament that takes place with both starting to merge into one. Every major cast member is involved and contribute in exposing the truth behind the Crane Master's plan. Be it Yamcha, Bulma, Oolong, Puar, Goku, Roshi and even Krillin.
However, there are way too many characters that only exist as lesser important characters because they appeared in the main story like Arale who just exist because the main story had a crossover too.

Overall, this movie is really mediocre by original Dragon Ball standards. It eats more than it can chew and that is its weakness. However, it still has some really good elements like how it uses its cast and the conflict behind the scenes. Also it has a fantastic ending and the best way Chaotzu has been treated in this franchise.