MassBlock provides a link to a modal (without changing location) which allows the user to list users to be blocked. As with conventional blocking, it requires administrator rights (or equivalent) to use.
By default, the script will block one user per second. If you'd like to modify that, add the config massBlockDelay before importing the script with your own number (in milliseconds) instead.
The option to use the Mass Block script will appear under your "My Tools" list (the toolbar at the bottom of your screen).
It also has an "Add Group Contents" button, which inputs a raw list of users in the usergroup that you select.