Mumford, who helped the Swans win the 2012 premiership, and Jed Lamb both made the move across town to the Giants at the end of last season.
If the Giants are any chance of upsetting the Swans at Spotless Stadium, they must put a clamp on some of their opponent's blue-chip midfielders, and Mumford has given a keen insight into some of their strengths and weaknesses.
"Mummy's been really good, especially being a ruckman and tapping down to the Swans' midfield for so many years," GWS co-captain Callan Ward told AFL.com.au.
"He's helped our mids especially with who their go-to players are, how they like to push off in the midfield and even around the ground, where they like to run to and stuff like that.
"He's been terrific. In the opposition stuff that we talk about every week, he's almost run the sessions himself.
"And Jed Lamb has chipped in a fair bit too. It's been really good."
Another of the Giants' weapons is key forward Jeremy Cameron, who is expected to overcome an ankle sprain and take his place in the line-up against the Swans.
The 20-year-old will attempt to follow up a season that yielded 62 goals and an All Australian guernsey, although he has a modest record in Sydney derbies.
He failed to kick a goal against the Swans in his AFL debut and managed just two over his first three games before kicking 3.1 at the SCG in round 16 last year.
Cameron expects to once again find Ted Richards for company.
"We've played on each other a fair bit, pretty much in every game," Cameron said.
"I'm looking forward to the challenge again.
"He kept me to about two disposals last game (in the NAB Challenge), so hopefully I can go all right in this one."
While the Swans will do their best to keep Cameron quiet, the Giants will have their hands full with Lance Franklin, who will make his official debut for his new club.
Franklin, who kicked six goals across his two games against GWS while a Hawk, is anxious to make a strong start, according to Richards.
"I've spoken to him about it and for the NAB Challenge game there was some nerves there for him," the defender said.
"Being at a new team he wants to get off to a good start and it's really good to see that no matter how long he's played, he's still got those butterflies and wanting to start the year on a good note.
"Unfortunately he only played half a game last week (against the Brisbane Lions before taking a knock to his knee), but in that half he kicked two freakish goals.
"I'd be happy if he kicked four (this week)."
There is also a palpable sense the intensity in the fledgling rivalry has been turned up leading into round one, and Cameron feels his side is a big chance of its first win against the Swans.
"For sure, we've improved so much over the pre-season," he said.
"Coming off the back of last year, we knew we had a lot of areas we needed to improve.
"We've got some new players into the club and they've shown a lot of leadership on the ground and we think we can match it with the Swans."
Twitter: @AFL_JD
