You can offer special prices and discounts for your event registrations via coupon codes. To add a coupon code, go to "Edit this Campaign" for a campaign in which you have the Registration tool active. Click on "Manage" Registration.
Here, you'll be able to add a coupon code, or multiple coupon codes.
The Coupon Code Title is itself also the coupon code. You can set it to either a percentage discount or a set dollar amount discount. You can also limit the max discount in case of a percentage, limit how many times the code can be redeemed, and set an expiration date for the coupon. These are all optional.
Don't forget to hit Save when done!