Mulligan, who turns 22 in just over two weeks, will play his first AFL game at Skilled Stadium in what is his fourth year at Whitten Oval.
Montgomery said Mulligan's presence in defence - and Barry Hall's expected absence - is likely to see Williams push up the ground in similar fashion to the way he did against Hawthorn on Sunday at Etihad Stadium.
"We're happy to keep experimenting with that. Tom is in the team for a number of reasons; a bit of coverage down back, he looks lively as a forward because he's got leg speed and every team is after that," Montgomery said on Wednesday.
"We gave him a run in the ruck on the weekend and he didn't disgrace himself either.
"We're looking at different things for Tom."
Williams kicked two goals against the Hawks, one in the second quarter and one in the third after Hall had been subbed off.
Montgomery said Mulligan, who hails from Queensland and has worked his way from the VFL reserves to an AFL berth, deserved his chance.
"He's really earned his spot ... he's done his time," he said.
"He's a tall defender and we need those at the moment, he's super quick which keeps him in the contest for a lot longer and he's got some real hunger and drive and aggression.
"Those are a couple of things that have been lacking in our game."
Adam Cooney, Ryan Hargrave and Brian Lake all trained on Wednesday at Whitten Oval, but only Lake is a certainty to play on Saturday.
Cooney and Hargrave will be tested later in the week to see if they've overcome knee and foot concerns that kept them from playing last week.
Hall was unsighted at Whitten Oval and is considered "very doubtful" after he "jagged" his bad ankle against the Hawks.
Montgomery said the momentum shift caused by the Dogs' avoidance of a blow-out against the Hawks after trailing by 46 points in the third quarter had influenced their training intensity this week.
He also said the Dogs' skill level, which has come under fire in recent weeks, was being looked at by the coaching staff and blamed its drop off on the changing nature of the game.
"It hasn't been the guys' ability to kick; it's been the more defensive mechanisms put in place, the numbers kicking through, the hands you've got to kick over," he said.
"There's a lot more things to worry about now when you've got the footy in your hands rather than just being able to execute.
"It has been exposed over the last fortnight and we're addressing it. It's not a quick fix.
"It's something that's going to take five, six, seven weeks to fix, and sometimes that's fixed at selection and not just on the track."
The Dogs will not elevate a rookie this week in place of injured 2010 draftee Tom Hill.
