Uhmm, do you know the dynamics of the dungeon? I guess you mean Abyssal temple. First boss requires:
. look carefully to not be in team: if you enter a dungeon with a grup, it automatically starts the team mode, and it's a lot harder than solo mode,
- you have to kill the second butcher, the fat guy in middle of the room with other mobs, before enter the boss room, if it's alive, it gives to Asura a regen buff forever,
- fight Asura near the spawned addicteds, take the HP of the addict lower than 3k hp, and it will give to boss a debuff for 20 seconds. Fight the boss, when 20 seconds are gone, move to another addict and do the same.
For any doubs, you can check some videos on youtube about how to win Abyssal Temple.