Powerful and intelligent is a deadly combination, especially for a BBEG. I'd be cunning and ruthless. My tactics would vary greatly, depending on whether or not the BBEG has lair actions, legendary actions, and henchmen, but I would focus on permanently removing opponents from the board one by one.
If the BBEG is a spellcaster: drop the fighter and then Misty Step to cover, making sure to stay in Counterspell range for the cleric's attempt to save him. Next round, double-tap the fighter, saving my reaction for the next incoming cleric or wizard nonsense, and demanding they surrendur. If the party doesn't flee or surrender, I'd steal the fighter's most impressive-looking piece of equipment and run away, making them chase me through my obstacle-course lair of traps, pets, and henchmen.
If the BBEG isn't a spellcaster: same story, except I'd drop the cleric first, then move to cover to escape the wizard/rogue's targeted attacks. Double-tap the cleric on my next turn, demand their surrender. If they don't flee or surrender, I would loot the cleric's most impressive-looking piece of equipment and run away, making them chase me through my obstacle course above, and harrying them at range every time they try to stop and rest.
But the best bet would be to use my action to disengage, then bonus action to Misty Step or whatever out of reach. Repeat as necessary until the party either breaks pursuit, or the only one that can keep up with me is the rogue. Then I'd turn on the rogue, drop him, then double-tap him, and then loot his body and flee once more as the rest of the group is trying to catch up. My escape route would have lots of twists and turns and blind corners to keep anyone from having a clear line of sight to me at any time, and lots of boobytraps and pets to make them regret chasing me. Then just when they think I've escaped, I'd double-back and attack them just as they're trying to rest. In short: I'd never let the fighter "get up in my grill" again, especially while I'm also easily targeted by both the wizard and the rogue. A powerful and intelligent opponent would try to gain and keep control of the battlefield and conditions long before any dice are rolled.