The area would be dark as would be the boss, so it kinda melts with the environment.
  1. some tentacle thing or something similar so it hits only players and all or most players in the area(i think bosses focusing just that one fae clone is just boring), also it grounds all players in the air for like 10 seconds or something
  2. snare or root or something. dark round matter appears on the ground, below players and something comes out so it roots the players
  3. a bigger AOE effect (dont care what is, like flames, heck I wouldnt care even if he cries and causes AOE damage)
    or make him cry big tears that when they hit a player, their mana goes down or something
  4. Make him fly, so hes not that of an easy target (for at least 10sec)
passive (something that heals himself, otherwise the fight is over too fast):
like leeches or something, more players around the boss the more health he regains

He can even summon minions and disappear until all minions have been destroyed and in the mean time heals (he heals more if more players are around ofc)

I dont really care what the name of the boss is or the name of his abilities for that matter, just make something that isnt defeated that quickly and is a bit more smarter in a fight, like who he focuses and what abilities to use at what time.
And ground the players more, jumping all the time like 20 times or more.