Coincidentally, both the Drumuru fight in WoW (Throne of Thunder raid) and Dread Master Brontes in SWTOR (Dread Fortress operation) share a very similar, yet unusual, mechanic. Let's compare the two implementations of this mechanic, and see which did a better job.
Both bosses have a phase where the boss stands in the center of the room and fires a beam towards the edge. The beam then sweeps around the room and players have to run around the boss, avoiding the beam. If a player is hit by the beam, the player instantly dies.
Drumuru differs by having a poisonous fog appear on the ground at the same time as the beam. There is a "path" through the fog, somewhat like being in a maze, and the players are supposed to follow that path as they move around the boss. The path opens up as the beam progresses, keeping the players in danger from the beam.
Brontes has six robots appear around the room. If the beam hits a robot, there is a massive explosion and everyone dies. So the players have to kill the robots in order, starting from the one closest to the beam and working around the room.
The biggest downside to the Drumuru version of the mechanic is that the colors chosen make seeing the path more difficult. The fog is dark purple in a dark room on a dark floor. It's a mechanic that people consistently failed on, even after several months. However, this was probably done to maintain difficulty. If the path was very easy to see, this would be a trivial phase.
The Drumuru mechanic is fairly artificial. The speed you move through the phase is restricted by the rate at which the path in the fog opens up, not by player skill.
The biggest downside to the Brontes version is that it is very much a mechanic where if one person fails and gets caught by the beam, the entire group wipes. For Drumuru, survival of the phase is independent for each player. (Thank God for that, else the fight would have been impossible in LFR.) One or two players dying doesn't affect the group getting through that phase.
The Brontes phase can be a little harsh on a melee-heavy group, since they have more running time to get from robot to robot. Drumuru had two paths, one for melee, and one for ranged.
All in all, the Brontes version of the mechanic is superior. For one thing, being able to actually see the battlefield is so much better than blindly running around in the dark. The fact that Drumuru never really saw improvement in survival rates over time (in LFR at least) is indicative that many players were simply unable to grasp the mechanic. The test of a good raid mechanic is "mastery", in that players learn the mechanic and continuously improve their skill at handling it.
The fog path is also an artificial "dancing" mechanic. Whereas killing the robots is a test of basic character skills like dps and positioning skills, while still maintaining the "threat" of the sweeping beam. The robots' health gives you a good measurement of how much you have to improve. Finally, you can see your group's improvement from week to week as you kill the robots faster and faster.
Drumuru vs Brontes is a good case study in how a single raid mechanic can be implemented in two different ways: one sucessful, and one unsucessful.