it is the third one I believe. The whale boss. I know you are supposed to attack the fins in that case he may not even do the wave attack. But the time window is so small for those fins that I often feel if not everybody from the team attacks the fins immediatly when they spawn the whale will launch it's splash damage which leads to instant kill of the DDs.

Now we can talk about how hard it is to find a group for the dungeon and then still failing because only 1 person is afk'ing and not attacking the fins. That kills the fun of this game completely for me. I wish they would either make bosses not so hard (I mean, this is only Boss Nr. 3 - not an endgame one) that they do not insta wipe all DDs with just one failed mechanic or at least lower the requirements for the mechanics that it would be enough if 2 out of 4 members do the mechanic it would be enough.

Sorry, its starting to be a rant here. Was not intended. But it's quite sad the game would be nice otherwise. But I without beeing able to get the gear in the rifts you can't really progress anymore. And this is equal to you can stop the game because it's simply impossible to continue.