Vajet is pretty much spot on with the list. We haven't killed Styrax yet, but in our few attempts he takes the prize for most difficult atm. Some few added points:
- Dread Guard nerfs have really made the fight much easier
- TFB has a tight DPS requirement (healing and tanking are fairly easy)
- Olox and Warlords have tough healing situations (I personally hate the first minute of Warlords
- Styrax and Thrasher is all around difficult for every class and usually 1 mechanic failure is a instant wipe.