England's eight-wicket triumph in Karachi completed an away whitewash against Pakistan for the first time.
And Stokes was there at the end, undefeated on 35, with opener Ben Duckett hitting an unbeaten 82, including the winning runs.
"Ben is always pulling a string somewhere and the guys follow him. It makes it pretty easy from the coach's box," McCullum told Sky Sports.
"We see what he does on the field, and there is a genius in a lot of it.
"He has got an insatiable appetite to keep moving the game forward. It's the pure passion and drive he has to make a significant difference.
"He is only going to get better, which is quite scary."
England had been set 167 to win on the evening of day three, and started their chase in a manner that epitomised the attacking brand of cricket played by the side, quickly reduced the required total to 55 overnight.
The pair quickly knocked off the total in just 11.1 overs on the morning of day four.
McCullum added: "What we have seen over the past seven or eight months is the skill and talent is not in question.
"All we try and do is remain consistent with the messaging, have a smile on your face whether things work out or don't, and encourage guys to allow their talent to come out without the fear of failure.
"I think we have taken 20 wickets in a Test on nine out of 10 occasions. You have got to be able to bowl teams out, and the mantra in the group is how do we get wickets?"
Stokes added on Sky Sports "The way in which the team goes about its business gives me so much confidence in myself. It is seriously special.
"I could stand you here all day and talk about individual performances, but I would have to mention everyone.
"When you take that burden off individuals and the team, you see players excelling and showing more within themselves.
"If the ambition (is) to win and play an entertaining brand of cricket, that's going to override any fear of failure whatsoever. When that fear of failure isn't there. you just make better decisions.
"Releasing that failure and fear off everyone is why we have produced the results."
Former England captains Nasser Hussain and Michael Atherton were left enthused by England's performances across the series.
"To get 20 wickets three times in a row, and the rate of runs, was incredible," Hussain told Sky Sports.
"Pakistan could not keep up with them. Everything they (England) have touched has turned to gold on this tour."
And Atherton added: "It is an incredible transformation. It has been a rapid turnaround, and I don't think anyone could have guessed how quickly it would come. It has been a great tour."