Millhouse Manastorm (the easiest boss). Spec: Marksman.
You won’t get instant killed by this boss.
Strategy: notice that Millhouse is spawning 2 “totems” from time to time. Stand in front of a totem to receive the channeling beam buff. Kill the other totem.
When Millhouse spawns the next two totems, move in front of another one and kill the other two.
Blow your cooldowns, drums of rage, brawler’s guild potion etc, after around 30 seconds since the fight starts.
Epicus Maximus. Spec: Beastmaster.
It has the lowest HP from all the bosses but can instant kill you.
Strategy: Pet growl on, misdirect on him. Once you start the fight, move left-forward to avoid that beam. Nuke the boss. When he is casting that blue thing (throws some blue stuff), interrupt him with Silencing Shot or Intimidation. Avoid the circles from the ground (these are pretty harmless).
Disruptron. Spec: Beastmaster.
Strategy: Jump over those red beams and nuke the boss. Notice that the area gets flooded with those circles when the boss has only a few hp left. That’s the perfect moment to blow all your cooldowns, don’t use them at start.
Zen’shar. Spec: Beastmaster.
You need to kill all the small orbs and avoid the beams. AOE the small orbs with Multi-Shot and Glaive Toss. Use all your cds except Stampede.
Once the small orbs are gone, kill the big orb. You still need to avoid all the beams, is not that hard.
I’ve killed all the bosses with 532 item level.
If you have any questions, leave in the comments.