Unlockable Quests feature came in Version 6.2.0 and added a new menu to the Extra Island. The Unlockable Quests menu allows the user to start a new quests at a time of their choosing. Unlocking a quest costs one gem, through first time finish has a gem reward, so the first use of this feature on each quest is essentially free.
Initially only quests for evolvers and boosters (penguins, turtles, etc.) were available to be unlocked on every day basis, but some events introduce temporarily available content (ex. during Halloween 2017 some Halloween FNs were made available in format, and later some clashes and other FNs), as well as unique quests to obtain character-specific crystal skulls.
WARNING: Please be aware that missions in which you can obtain legend-specific skulls, like Germa, Eneru or Judge are relatively difficult, roughly corresponding to harder 30, 40 and 60 stamina difficulties. Do not attempt them without reading a guide. The other quests are very easy and you should be running either Buggy for extra drops or an EXP captain if you are desperate to level up.
Content uniquely available through UQ:
Occasionally (available a few times each year for several weeks at a time):
- Chopper and the Cotton Candy Paradise
- quests to acquire specific ships for 30 gems (Zunesha, Hoe, Megalo, Germa 66 Ship). Very easy and drop items like +50 candies and good manuals/tomes.
Always available:
- Higuma Mountain Bandit at Sea
- Forward! Straw Hat Pirates (Sanji version and Franky version)
- Germa Resurrection Plan
- Germa 66's Counterattack!
- Kami Rises Again!
- Unlock! Manual Paradise - drops quite a few manuals, may be good for new players (whales...) who don't have many generic books and don't want to farm old quests
- useless turtle quests, you really should not be wasting germs farming those