So the lightning phases at 90, 60 and 30 revolve around the marker and it is the most important role here.

The markers role here is to keep feeding the boss the chain lightning buff which damages him and makes the dungeon a whole lot easier and the 2 and 3 man conduction teams are here to keep this marker person alive. When the boss targets a person to be the marker, he will at first spawn 2 lightning balls which will allows follow the marker. What is important to know is that a single person can take a combination of 1.5 worth of lightning (chain lightning is counted as 1 and the lightning ball is counted as 0.5) meaning that you CANNOT take more than a lightning ball and chain lightning otherwise you will die. For the first lightning, the marker and #2 will tank the lightning ball and then boss will target the marker for a chain lightning attack. This attack will 1 shot the marker unless there is at least one other person near him to share the damage and at this point they both have 1.5 lightning stacks and cannot take anything more. So the boss should grab the marker, eating the chain lightning (but not the lightning ball so he still has 0.5 here), second lightning the other 2 people for the 3 man conduction switches to tank the lightning balls because the marker can't take it (0.5 + 0.5 + 1 and he will die) and then they will all share the chain lightning (so they have 1.5), marker gets grabbed and at 0.5 again. At this point you will need to to CC the boss for at least 6 seconds to allow the lightning to wear off from #2 so that he can take the third lightning ball and chain lightning (marker should be at zero so he can take both again)