-Lure it to the entrance corner first, then dps it (leech sword is a must).
-Strategy: Stay away from shroom (spawn every 10 sec, effect range: very close); just go behind the boss would be enough. Get 1 range dps lure those Gaint (spawn after boss hp down to 50%). The range dps pay attention to the shroom army (spawn after boss hp down to 25%).
P.S: Since boss in the ent corner, main boss dps dont have to worry about shroom army.
-Lure it to the entrance corner first, need at least 2 healer fast cast spd spam aoe heal most of the time and rev. And 1 person to tank mobs that spawn.
-Stratedy: Well, after enter click on the star icon on mini map and finish the even for boss to spawn, then just bruteforce is all I have to say.
P.S: Stay away from those touch, even if get stun by it, just leave it be, it will disappear after a bit. DPSer will get stun from boss (cant be removed even with PP debuff).
-Nothing to worry about mostly. Click on the star icon, and finish the event until 4 sub boss spawn.
-Stratedy: Stay way from the "Greatsword" mob when he spawn along with 3 other mobs (has debuff -20% def ea hit, stack up 20 time), use Range or Magic to dps this one, remember to spam ROOT/LOCK on this. After that boss will spawn, and just full dps it, nothing much to worry at this point.
Above just my personal exp about boss fight. U should ask around more for more tips.