I am concerned that they will mop the floor with him and I want this fight to be epic. I do know that one issue will be that the party ranger will delay his action until BBEG begins casting then shoot the crap out of him with his dominant bow thereby disrupting his spells.
I do plan to change up some of his spells to better protect him, especially since the alchemist will be lobbing dispel bombs at him relentlessly.
Any suggestions? Any way to help against the arrows? I am interested on how this fight went with other GM's