If you want a Scottish Dragon,
you must find one, bow to it and then right-click
it and not get off. You also must 
have some meat in your hand to tame it.
Just remain seated and wait.
If you tame one, it will 
not breathe water but it can be very strong
in interaction with Pegasi. 
Keep in mind: if you forbid 
it to fly, it will not be able to attack.