While merging incidents is a good idea, if you want to resolve a lot of incidents at once, you can do this by creating a report and using mass-actions.
Incidents > Reports & Queues > select a report > select the incidents on the left-hand-side > add mass actions to perform.
From here you can set the status to "Resolved", close the incident and add a comment all from this screen. Notifying the watchlist, and the customer if you want.
You can also report on all incidents linked to another service desk record by using the "Linked To" condition. Allowing you to report on all incidents linked to Problem or Release, this may come in handy if you find a workaround for a Problem and want to update all the associated incidents, or if a Release addresses a number of incidents.