The Mystery Duel is one of the new game modes that have been added to Overwatch since the introduction of the Arcade, last patch. In Mystery Duel, two players battle each other using the same, randomly chosen, hero. This mode saw a lot of action since the patch; so much that Blizzard is considering to expand on the ideas of 1v1 duels some more.
Jeff Kaplan, Overwatch's game director, explained in the official Battle.net forums that Mystery Duel is merely an example of what Blizzard is planning to build on the concept of 1v1 fights:
We have lots of ideas for other 1v1 modes. Mystery Duel was just the first expression of what we want to try in the 1v1 space.The fact that Blizzard is planning to expand on the concept and bring more 1v1 modes is good news. After all, TechRaptor pointed out the lack of variety in game modes when Overwatch first came out. It's great to see the developer working to bring more choice on the field.
Also, eventually in Custom Game you'll be able to do a 1v1 with your friends where you can select the hero pool (meaning the available pool of random heroes that Mystery Duel chooses from). This is a feature we're actively working on right now.
On the topic of Mystery Duel, Kaplan explained why Blizzard decided to remove Lucio and Mercy from the hero pool of the 1v1 mode in a different thread:
We removed Lucio because the battles (if played a certain way) would always end in a draw. Also, when we buffed Mercy, she ran into a similar situation.Given the kit the two support heroes have, it's understandable how it would be feasible to bring the whole game to a halt while using them.
We have some other ideas to solve these problems that we’re going to try in future iterations. Hopefully, if those changes are successful, we can bring Lucio back.
Kaplan also addressed the issue with Ana in the 1v1 mode. A bug prevented the medical sniper in showing up in the vast majority of games. Kaplan also promised that said bug would be fixed soon.
Do you play Overwatch's Mystery Duel? Would you like to see more 1v1 modes in the game? Let us know in the comments.