However, the most fitting in the game would be 8 man dungeon designed specifically for armoury system. A dungeon where changing jobs inside is allowed, and every encounter requires different party composition. Of course having to complete it with same players from start to end. Example fights:
1. boss that deals 6k damage to 6 players with highest enmity every 20 seconds. Alternated with an attack that deals 6k damage to single target from 4 of highest enmity, marked 5 seconds before.
2. Flying enemy that cannot be hit with melee attacks.
3. Boss that reflects magic damage.
4. Boss whos attacks reduce maximum hp. Ignores stoneskin, succor and adloquium.
5. Fight against 3 enemies that does high damage to single target, and each does an attack that increases damage taken for 15 seconds, every 18 seconds.

Only enabling elemental weakness and resistances would greatly increase the possibilities.