No-Dupe Champ Crystal
A basic 5* crystal that only pulls champs you don't have.
Considering custom champ pools are being worked on, this should be possible. Eventually. Maybe. After this many years the code has gotta be deep-fried spaghetti. There's also no reason for Kabam to be nice unless the weight of soul-crushed champ chasers quitting on the 4th Groot in a row is high enough.
Still, is this something you'd want?