Obtain the required in-game progression for the Cursed Child questline
Speak to the NPC that starts the Cursed Child-related quest
Complete the required quest objectives
Defeat the required boss or enemy tied to the unlock
Collect the required item drops or quest items
Return to the NPC to claim Cursed Child
If the game uses a shop or roll system, obtain enough currency or spins and roll until Cursed Child is unlocked