Hello:
Mountain Horned Dragons are fairly fiesty animals when they are in good condition. I have seen them threaten with the mouth slightly opened on many occasions. You have to be careful though to be sure that the animal does not have a respiratory problem. Weazing and/or mucous in the mouth would be obvious signs of that.
There are many Horned Dragons out there that are missing the spines above the eyes. This is common and i personally have never seen them grow back. If the animal you have is a youngster the horns may not be all the way in yet.
Hope this helps.
Have A Great Day!!!