Mass Deleting Email Templates

You can! All you have to do is this - 

1. Login to Dataloader.IO [ http://dataloader.io ] with your Salesforce Credentials.
2. Click New Task to select Export
3. Select the Object as: Email Template
4. Select the Fields: Id(this is required), Name, Subject and all the other fields that will help you identify the ones that needs to be deleted.
5. Click Save and Run
6. Now, you should see an CSV file that will have all the Email Templates.
7. Open it in a Spreadsheet Application of your choice.
8. Retain all those rows which has to be DELETED.
9. Now, login to the same Dataloader.IO
10. This time select New Task to opt for Delete operation.
11. Upload the CSV(the one that you formatted in step 8)
12. Click Save and Run

That should do it!