Yes all of these would be good but I think that your third suggestion which was:
"3rd and final suggestion; a minigame in a dark kind of place and the players must kill a certain amount of undead npc's to finish the round, the rounds reward points which will be used to buy the custom item(s) of your choice(or whoever makes them) and the items can only be attained through this minigame."
This would be good for dungeoneering because a round is like a floor. The points could be tokkul and the customs is the dungeoneering shop
