>>33809949Supposedly, there's a part of that myth where one particular dragon was stripped of its draconic powers by the Gods because it went on a rampage. However, I cannot find a single origin of this tale, so it's best to assume that's fake.
The more likely reason is because a Water/Dragon type in Gen I would be absolutely broken. The only damaging Dragon type move did fixed damage; it would've had 0 weaknesses.
