Here is a blog which has come up with all my experiences revolving around mass delete in Salesforce.Following you will see the topics/ways on mass delete.
Standard Mass Delete Records Feature
You can delete multiple reports or records at one time.This Feature is available on Salesforce Classic as well as Lightning Experience and in all the editions.You can start by navigating to Setup, enter Mass Delete Records in the Quick Find box, then select Mass Delete Records and click the link for the type of record to delete.Here are the well explained steps to achieve it .Also,Please note that the record types you can mass-delete include cases, solutions, accounts, contacts, leads, products, and activities.I would recommend you to go through Important Notes on Using Mass Delete
Mass Delete Dummy Data In Salesforce
The dummy data is the data that includes Accounts, Contacts, and Opportunities which is provided to demonstrate Salesforce functionalities when we start a trial version or subscription .However,there are times we need to delete this dummy data as to ensure we do not get confuse with real org and dummy data.Here is Step By Step Guide to perform this requirement.
Custom Button for Performing Mass Deletes
Truncating Custom Objects
One of the fastest way to delete multiple records in an object is using TRUNCATE on the object. It will delete all your data in that object.
Please have a look here for more details.
Delete Records From The Developer Console
You can rule this line in execute anonymous and booom…
delete [SELECT Id FROM MyObject LIMIT 10000];
Mass Delete Records using Data Loader
This is the most awesome and recommended way which is used by almost all the admins to mass delete data.I would not repeat the lines to explain this as we have a lot of explanation available for deleting data using data loader
Using Premier Support Plan
If you are Premier + support plan, salesforce offers Administration services as part of the plan.Please refer to the link for more details.
Other Tools To Explore
Also there other tools like Jitterbit Data Loader for Salesforce,Dataloader.io,
Demand Tools and Informatica Data Loader which can be used to delete records.
Hope you like this Blog,Please write your comments in case you want me to write something more here which I might have left.