Maybe add a quest system to the world boss that players can manually choice depending of their gear/build/level while adding challenges suggested above.
For example, players can choice to be killers, assistance, deploy, healers, etc.
Killers would gain an extra cube for dealing a % of the WB health while gaining another cube when the WB is killed while healers would gain an extra cube for having X number of heal tiles consumed( Rewarding the healers to heal non-party members) and adding challenge of deploying obstacles to debuff/damage the WB.
All rewards should be given upon the death of the WB with the extra cubes. Also adjust the rewards, they are quite bad.
