I'll follow up with a
Komodo Dragon. A bit unusual, but this type of game needs some sort of a dragon for Knights to fight, and this beast fits the bill.
Yes. yes, I know. Not something associated with feudalism in Europe but there are other aspects of the game that don't fit either (like scale armor), or natives for that matter. They did exist during the feudal area though, and who knows, perhaps some of the stories of dragon fights were based on encounters with these creatures.