‘Super-complete Rewards’ are an extra set of rewards that you can complete after you complete the rewards progression in a Hatch Dragons event.
Once an event is completed, new goals will be available to work toward. These goals are a ‘hard-mode’ challenge, so they are tuned up to be 50% more difficult than the base event! For the dedicated players who want to keep striving for a few extra rewards.
For clarity, this does NOT affect the base event at all! The difficulty increase is solely for the Super-complete Rewards section of an event.