In all dungeons so far, you need to beat the Boss to get the Dungeon Reward,.
In this Dungeon, you will be randomly spawned on a map with the Boss chasing you.
In the beginning the boss will be quite harmless or slow, but also immune to all damage types.
You can either look to loot some of his treasure and escape or look around for shrines, which disable on of his damage-types.
(Though to escape you will also need to find the exit of course, lol)
There will be a shrine for each of his damage types, but will you find the one you need in time, as the dooming boss gets stronger and stronger?
Also, each time you loot one of his treasures, the boss gets a random buff. (Gets stronger)
If you kill the boss, you can loot all of his treasures. (They will be summoned to you)
Bonus:
There could be a special reward if one manages to kill the boss after looting all his treasures.
Dungeon Ability:
A random teleport with limited uses. Decreasing with each tier of the dungeon.
Will you use it to escape from the boss or to look around for the treasures?
The choice is yours to make.
(The teleports could slowly recharge over time, if needed)
TL, DR:
Imagine a damage invulnerable Exiled Mage-Boss chasing you and trying to kill you, while you look around for treasure chests.
You can disable his damage-type immunities if you find the shrines.
There will be a shrine for each damage-type.