Mechanics:
Around 75% of 2nd drake HP bar, first drake will cast poison tail in 1 or 2 players of your party. Those 2 players must run to the wall away from the party and away from the bosses (15m), the rest of the players without poison go stack with the player tanking first drake. Wait until boss casts Penetrating strike, this a damage shared skill. After that 2nd boss will pull you all, Cleric must dispel and you must run away from the boss and wait until he casts Losing Rationality. After the cast is done you can go back to DPS boss. These are the only mechanics of the boss. Depending on your DPS you will get several waves of poison and the shared damage skill will start to do more and more damage until the point you can't tank it, so this is a DPS race.
TIP: You don't need to stack for the first wave of poison as the first Penetrating strike deals close to no damage.
If you have any doubt feel free to comment.
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DPS Meter:
Raging Barkhan Forbidenx-Storm: 21,774,084, Eraze-Storm: 15,988,452, Drunkshotzz-Sillu: 8,891,805, Edgarjc-Storm: 6,577,659, Blaziken-Storm: 865,799,
Raging Yarkhan Devrost-Storm: 16,634,594