Starman
Adventurer
Take a page from Trailblazer. It has a template called 'Solo' for the big bads that the party faces. Without adjusting the CR, you multiply the creature's HP by the number of members in the party. Then you give it a number of action points equal to the number of party members. Action points can be spent to improve a d20 roll, negate a critical hit, auto confirm a critical hit, use a limited resource ability (e.g. "per day"), and a few other things. It's a great way to beef up your BBEG.