Narma and Fayne, for sure. And to be totally honest, I don't think I'd bother with the first FB. Narma does everything she does, and also extends debuffs. Does your friend have Ninja? I'd say he'd fit better.

Ninja or even Coffin Smasher if Ninja isn't available.

Why Coffin Smasher? I think he doesn't need atk down, it's an unkillable combo. Roshcard for two turns unkillable with a 3 turn cooldown, and Torturehelm as target for the stun hit when no unkillable buff is actice - Torturehelm dies, but gets revived from his passive.

I  like  the  pick  of  Coffin  or  Ninja  here.    In  the  comp  you  proposed  youll end  up  with  too  many  poison  procs . Adding  an  HP  burn  is  going  to  provide  A  new  source  of  damage  and  keep  your  debuff  bar  more  manageable    

HP burn my friend. As a rare, likely to have on the roster. Plus easy to book as a rare. Smasher's damage is HP based, so easy to build. Also provides a good champ for FW, so it's not a wasted build either, when and if you upgrade to some other burner later.

you can only land 10 debuffs on the boss, if he's maxed with poisons already, a 3rd poisoner won't add anything and might even prevent attack downs or def downs from landing if his bar is full of poisons.

i'd go a different direction like others are saying.

Don't forget about Narma A1, though. The debuff extend makes it much easier to stack 10 debuffs and not worry about the wrong ones falling off and not being replaceable.

Thank  you  all  so  much  for  the  insight!  Good  call  on  the  too  many  poisons!