I would like [mini] dungeon challenges whereby strong monsters with one certain DoT skill need to be beaten to claim the reward at the end of the challenge.
This way, immunities to certain DoTs will play a bigger part in the metagame.
You could have a Poison Dungeon, where all the AI monsters will hard hit you with poison - therefore you bring out your best Immune to Poison team to counter the AI. You don't have to use monsters immune to poison, but the dungeons will be very difficult to beat otherwise because the AI is very strong.
A rule of the DoT dungeons is that no Artifacts allowed.