For example
Open all your idol slots.
Kill Majasa.
Reach X faction level.
Complete conditional boss kills.
Finish dungeon challenges.
Complete crafting challenges.
Reach level 100.
Reach X Corruption.
Create your first 4-modded legendary item.
Use X rune to craft.
Bonus season themed challenges.
We can think of a dozen more. They can also encourage players to try newly added content through challenges, such as defeating a new boss or using a new crafting method. It’s a win-win.
Rewards don’t have to be amazing; it’s just another option to encourage players to push harder.