Question about mood changes. is it the type of mood or amount of change that makes it bad?

Depends: The question is a little vague. For example, it is perfectly normal to become joyous (from feeling sad) after hearing very good news or vice versa after hearing really bad news. However, if ones mood changes dramatically without a clear trigger (getting furiously angry with no trigger for example), then seeking an evaluation may be useful.

Amount: More importantly, how do the changes negatively affect you, people around you, and things that you do every day.

Degree: It is the degree of mood change that can be problematic. Sad and elated feelings are healthy, but when they become extreme they impair other life activities. In depression the person may lose interest in things or be unable to function generally because of extreme sadness or unexplained body symptoms. In mania, the functioning is overly speedy, impulsive, and easily angry or irritable.

Mood changes: Extent, frequency & duration of changes, age of onst, as well as response to treatment.