McGregor says the key is that Marshall is happy again, and the New Zealand international puts that down to two things - his brief dalliance in rugby waking him from a lackadaisical slumber, and Widdop.
"I probably lost that motivation and hunger at the Tigers from just being lazy and not caring as much," he added. "Not taking as much pride in the performance. I was just there for the boys at that time.
"Now I want to be the best player on the field again every week. I haven't felt like that for a long time."
While there were glimpses of a blossoming halves partnership at the Dragons towards the end of the 2015 season, Marshall believes as a partnership they're now ready to take the next step.
Because in Widdop he has the sort of assistance he craved at the Tigers ever since the departure of Scott Prince for the Gold Coast at the end of the 2006 season.
"(At the Tigers) I had a lot of pressure on me to do a lot of stuff," he said. "Whereas with Gareth, we try and have 50 per cent share of the ball. And just try and take the pressure off each other.
"He's right up there (with the best I've played alongside)."
-AAP