The Players' Guide to the Cities/User Interface/Help Window/Flashback System

The following is from the Flashback System tab of the Help Window

Ouroboros

You can reach Ouroboros via an Ouroboros Portal as long as you are level 25 or higher. You will receive the power to create Ouroboros Portals by being exposed to time travel either through completing certain missions or earning particular badges but you may enter Ouroboros via your own portals or the portals of others.

Within Ouroboros you can learn more about time travel and also use crystal pillars to Flashback to your past to replay past story arcs and other notable missions.

Flashback

Visit the Aspect of the Pillar crystals within Ouroboros to activate Flashback. All the missions available to you will be listed, grouped by level. Any story arc or mission you have already played will have a gold star in front of its name and the name will be in gold and everything else will be in white. Clicking on a name will show you the contact and the introduction to the mission. If you accept the mission you'll be taken to the Challenge Settings page. Once you've chosen your Challenge Settings the Flashback is underway! Clicking on the big crystal will always transport you to the mission contact.

Once you're in Flashback mode you can't invite anyone to your team and if team members leave the team they can't rejoin, so it's best to get any teammates invited before you set up the Flashback. While you're in Flashback mode your other contacts are unavailable to you so if you want to stock up on Inspirations, visit Mender Roebuck in Ouroboros.

Challenge Settings

You can increase the difficulty of Flashbacks and Task Forces by selecting Challenge Settings. By customizing these settings you can add a time limit, limit the number of allowed defeats, disable certain powers, weaken yourselves, strengthen the enemies, disable the Enhancements in your powers or prevent the use of Inspirations - in whatever combination you feel daring enough to try. Succeeding Challenges provides rewards (except on Flashback for single missions) depending on the settings and the level of the Story Arc or Task Force. Failing a Challenge does not end the mission, it simply forfeits the reward. At the end of the Story Arc a summary page shows you how you fared.

On the Challenge Settings page you can select the Gold, Silver or Bronze time limit (or leave the default of no limit). You can select from unlimited lives, or from zero to 5 defeats permitted during the Story Arc. You can disable Temporary Powers, Ancillary/Patron Powers, Travel Powers (which will prevent all travel-like effects including Speed Boost) or everything except for your Archetype Primary and Secondary powers. You can debuff yourself and any teammates, which will weaken your damage and make you more susceptible to enemy status effects. You can buff the enemies on mission maps, which will strengthen their damage (among other things). You can disable Enhancements, which will make all your powers perform as if you had no Enhancements slotted, including disabling any Invention Set Bonuses or similar things. Lastly, you can prevent Inspirations from being used.

Each of these categories works independently and they can all be turned on at once.