>>715338931Dracomon's line debuted in World Championship, but is normally unavailable before you beat the game and unlock the area where you can catch him.
However, Otamamon and Dracomon share the same Baby II form. So, if you wanted to use Slayerdramon or Breakdramon in the campaign, the way to do it was to catch an Otamamon, neglect it to death (ideally you set up a torture room full of rotten meat and make it sit there after you have it fight Megas/Ultimates so it that gets badly injured), and hope the baby form evoles into Dracomon's baby form.
If it doesn't work, delete the thing, catch another Otamamon, rinse and repeat. Maybe you can also save scum it, but I'm not sure if time-based evolutions like those of baby stages are pre-determined in World Championship.
Ever since I learned of this, Otamamon became one of my favorites, partially out of pity.