Stopping com.mysql.mysqld from launching over and over and over agin
The script gets reloaded at boot because of RunAtLoad flag set to true in its plist.
Try unloading the script with following command, so it doesn't get picked up again.
sudo launchctl unload -w &lt;/path/to/com.mysql.mysql.plist&gt;

I don't have MySQL installed, so I can't tell exact location of the plist. Generally, it should be in /Library/LaunchDaemons/com.mysql.mysql.plist.
If not, look into following locations also and replace path in command:

~/Library/LaunchAgents
/Library/LaunchAgents
/System/Library/LaunchAgents
/System/Library/LaunchDaemons