Dorumon: evolution tree
Fresh -> In-Training -> Rookie -> Champion -> Ultimate -> Mega -> Ultra hierarchy as told in Digimon Chronicle, with Dorugoramon, the line through Reptiledramon and Grademon to Alphamon, its Ouryumon Jogress into Alphamon Ouryuken and the Death-X line to Dexmon, plus the film's own step from DoruGreymon to Alphamon.
Digivolution triggers
Alphamon Ouryuken: Jogress partner
Alphamon turns Yuji's Ouryumon into its sword (Digimon Chronicle)
Lore notes
the stories behind the unusual arrowsKing Drasil's Experiment
The Reference Book presumes Dorumon to be an experimental Prototype Digimon with a legendary dragon's life force deep in its DigiCore. In the film, Magnamon reveals it is King Drasil's experiment.
Two Tamers
In Digimon Chronicle, Kota and Yuji reach the New Digital World and partner with Dorumon and Ryudamon; their Digimon Pendulum X reads the X-Antibody through the XAI System and fires X-Cast attacks.
The Empty Seat
Alphamon holds the Royal Knights' Empty Seat and never shows itself. In the film, DoruGreymon digivolves into it while dueling Omnimon, and the knight the others knew only from myth appears.
Ouryumon Becomes the Sword
In Digimon Chronicle, Ouryumon dies shielding Alphamon from Dexmon, and Alphamon turns its data into the Ouryuken sword. In the film, Alphamon takes this form without Ouryumon.
Two Origins of DexDorugoramon
In Digimon Chronicle, Dorugoramon falls to Omnimon X and Death-X-evolves into DexDorugoramon. In the film, King Drasil builds it from Dorugamon's copied data, and it lays the DexDoruGreymon eggs.
The Empty Shell
In Digimon Chronicle, the management system pulls Dorumon's life data out of DexDorugoramon, but the empty shell lives on as Dexmon, a program with no DigiCore that even Omnimon X cannot delete.
Raised Again
Separated from DexDorugoramon, Dorumon starts over as a Rookie in Digimon Chronicle, and its Tamer, Kota, raises it again, this time through Reptiledramon and Grademon to Alphamon.
Back to Dorumon
In the film, Alphamon Ouryuken finds that Dexmon, made from its own data, is its other half. It impales them both, gives its X-Antibody to Omnimon and merges with Dexmon back into Dorumon.