brazen gulch
Illuvial collections could act as passes to get on leaderboards. This will get gauntlet/arena players trying to create complete collections. Each leaderboard has increasing rewards based on how hard the collection is to complete.
For Example:
If you have all tier 0 illuvials you get put on the tier 0 leaderboard.
If you have all tier 2 illuvials you get put on the tier 2 leaderboard.
You would be able to be on multiple leaderboards at once and collect the rewards for all that you are on at the end of the week.