[SixOfSpades]

Casting a Protection from Magic spell on a Dragon is a pretty dumb thing to do, actually, unless they somehow happen to be a Dragon that casts a lot of offensive spells.

Let's take a look at a Dragon onder the effects of a Protection from Magic scroll.....
Their claw attacks--nonmagical, so they can use it.
Their breath weapon--nonmagical, so they can use it.
Their wing buffet--nonmagical, so they can use it.
Your Lower Magic Resistance--magical, therefore blocked.
Your Greater Malison--magical, therefore blocked.
Your Finger of Death--magical, therefore blocked.
And so on, and so on.