What about Buddhists, Mormons, Muslims, satanists, Jehovah's witnesses, etc.?

correct me if I'm wrong, but I'm pretty sure Mormons are Christians.

Not really. They believe the Bible is flawed, and that Joseph Smith is a prophet who fixed the Bible 1800 years after Jesus was around. They also believe that Native Americans were Jews, and they wiped out another tribe of Israel, and were cursed with red skin. Also, they think seagulls are blessed/blessings.

But they believe that Christ is their Savior correct?
Mormons=Christians.
just with some other wierd stuff thrown in

There's also other things that are kind of necessary to be Christian, and some of them are a bit different. If you ask Christians, they'd say they're not Christian, if you ask Mormons, they'd say they're Mormon or Christian, if you ask neither, they'd say they're Christians.