New type of in-game menu,
where you can see all of the heroes from family/ realm.
It only shows your owned heroes and empty slots + max number of heroes from that realm.
Each owned hero in legendarium also shows his full 4:80 version AND extra bonuses from his family. So you instantly see, how much Ursena improves with 20% boost from 5 atlantis heroes (example).
Legendarium also provides new quests with rewards.
For example : Collect 3 heroes from Asgard realm, Collect all heroes from Asgard realm, collect 1 4* hero from each realm.
Rewards would be increasingly good in comparison with the difficulty of quest 
For example, filling complete roster of Atlantis heroes, gives you 1 pull of coins for each unique Atlantis hero (if there are 8 atlantis heroes, you get 800 S2 coins. Since you already got whole family, you dont really profit much from it
Simple QOL feature
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