While Dragoramon is not directly a Legendary Digimon by any means, why it is not considered such is an absolute mystery. It has done more legendary business than nearly every other Digimon known to exist, having altered timelines to suit it's Master's ideals to ensure no conflicting elements occur in the B/C universe when it was created by his master ages before he existed. By all means, however, most of this work is attributed to Rainboramon, the lesser known Champion Stage of Dragoramon. The reason it is not a Digimon of Legend is because all memories relating to it's history altering actions have been erased as if it had never existed in the first place. Rainboramon's very existence puzzled those who managed to tame Dragoramon and force it down to it's Champion Stage, but at the same time events that were meant to be long forgotten slowly became to be remembered... It is much more colorful than Dragoramon is for some unknown reason, possibly meant to represent the fact Rainboramon speaks regularly and has a personality compared to the silent and emotionless Dragoramon it becomes.
Digimon World: Bronze and Cobalt Versions
Rainboramon is only seen in the main storyline if it is faced first out of boss quartet, and if not faced until the very last, it and it's Ultimate stage will not be seen until Dragoramon is obtained and a special cutscene is unlocked for view in the gallery, actually a movie animated using B/C's graphics explaining the changes done to other universes by it's own actions. Though one would not see any viable need to degenerate Dragoramon down to it's Champion or Ultimate stages, it is ONLY by this manor does Dragoramon learn it's two vital traits that it has when faced as a boss: (Champion Trait: Decreases MP usage greatly) (Ultimate: Increases Power Level by 1 interval). These two traits not only aid Dragoramon in battle, but makes it's power level equivalent to that of Theridramon as a Mega. The latter trait is similar to traits other certain Digimon are known to have as well, with the former being a common trait among certain Digimon as well.
Rainboramon, after having been created by The Grand One, immediately wants to prove his loyalty to his master and so steals vital DNA of the most powerful being alive and begins to experiment on it and Yggdrasil's DNA, resulting in the creation of Terranadramon. Before this, however, it is chased around the universe by a Galacticmon that kept guard of the DNA strand from this mighty creature. Rainboramon is a highly unstable Digimon already, and as Rainboramon flees to several different universes, it results in several different changes occuring throughout many universes:
-The erase of the events of Young Hunters as if they had never happened, and that Tagiru never existed. The events of Xros Wars, however, took place normally. Young Hunters is a mere alternate timeline as mentioned by any Rainboramon if an Arresterdramon has recently been added to a DigiFarm. He'll go on to say, however, that he didn't cause the destruction of certain characters and timelines directly. None of the changes except for the ones relating to the Adventure 02 Universe happened to his own plans, so most of the changes seen from B/C can be attributed to accidents or paradoxes due to the entire Rainboramon line's unstable nature.
-Leomon still being alive in the Tamers Universe.
-Leaving a stable dimensional rip between the Data Squad Digital World and B/C's Digital World allowing travel between both easily.
-Gaining almost enough energy to digivolve to Goradramon.
-Causing several B/C exclusive Digimon to inhabit various other universes, as ALL B/C Main storyline Digimon were descended from this Digimon. SuperMechadramon appearing in the Adventure 02 Universe, the False Sovereigns in the Tamers Universe, Theridramon in the Frontier universe, Cobaldramon in the Data Squad Universe, an entire army of Nagadramon and XILA-Mon lead by another SuperMechadramon in the Xros Wars universe, among other things appearing outside of these more major instances.
-A freak accident that nearly destroyed the Digimon World: Dawn and Dusk universe by a mass summoning of 5 Lucemon Shadowlord Mode. This, however, ended humorously since all five of them were too focused on destroying each other than destroying everything else. Not only that, but they were all feral minded at best.
-Minor or severe personality changes in the main characters of certain seasons.
-T.K. marrying Kari in the Adventure 02 timeline, and although this occurred after the issue was resolved, it is still attributed to Rainboramon's actions in that universe.
-Giving an excuse for Matt's sudden career shift from a rockstar to an astronaut, due to the Galacticmon it had defeated on it's long voyage from trying to flee so much the whole time.
But the most important of the changes caused by Rainboramon, however, take place 8 years after the defeat of MaloMyotismon in Adventure 02. After having been chased to several different universes already and decided that the situation was getting nowhere, Rainboramon sends Galacticmon crashing down to Earth in the Adventure 02 timeline, and thus the storyline of Ultimate Endgame: The Rise of Dragoramon take place. During what would be known as the Terranadramon crisis, Rainboramon digivolves to Goradramon and then finally into Dragoramon inorder to aid the DigiDestined in stopping the overrunning Terranadramon. It also changed the final stages and evolution lines of the main cast Digidestined's Digimon as well to be different Digimon, as seen on Shiramu-Kuromu's digivolution userpage.