Q: My magic mouse is jittery and uncontrollable. I am on a MacBook Pro, 10.10.4.  I have cleaned everything, changed batteries.  I don't have any other bluetooth items near my laptop. The Magic Mouse is about 4 years old, never had a prior issue.

Hello Dustin,

It doesn't have to be bluetooth items that cause interference.   A modern smart TV the other side of the wall, a new home phone hub or a smart refrigerator in the room below.   Have you had any new electronic equipment in the house recently? 

Do you have more than one mouse, say, one with another computer.  Have you read these Apple notes on the subject?

Installing Yosemite has been reported many times as the point at which mice or trackpads become unstable.   I have read nothing from Apple to suggest it is a known fault point. But things change around the home and even the individual. 

It is always worth reading these two Apple documents carefully as a starting point.

https://support.apple.com/en-us/HT203171

https://support.apple.com/en-gb/HT201542