Marquise Goodwin has missed the past two games after being excused from the team to deal with a personal matter. He returned on Monday and practiced with his teammates on Wednesday.
"That's big time," Mullens told reporters when asked what it means to have Goodwin back. "Marquise, obviously, is a threat with his speed but he's more than just a speed guy. He's a great receiver. He's made a lot of plays for us, and I think he brings good juice to the locker room.
"Obviously, we just hope the best for him, the things that he's had to go through, but it's awesome to see him back in the building and out there in practice. We're pumped to have him back."
Broncos head coach Vance Joseph was asked during a conference call on Wednesday about Goodwin's impact on a game plan.
"He has true speed," Joseph told Bay Area reporters. "When you have a guy like that on the field, it definitely affects the play caller. It affects your secondary; how they play him and what calls they make. It takes one play for a guy with his speed to make a big play. So it definitely affects your game plan. It affects your play caller, and it also affects the players on the field when you have a guy with that kind of speed on the field."
Pierre Garçon has missed each of the 49ers' past three games and four of their last five. He practiced on Wednesday but was limited as he continues to deal with the knee injury that has plagued him for most of the season. Garçon was limited during each practice last week and eventually ruled out against the Seattle Seahawks.
Even without his two starting wideouts, Mullens threw for over 400 yards against Seattle, a milestone for the second-year quarterback.
"I didn't know (I threw for 414 yards) until after the game," Mullens said. "I guess it's cool, but we didn't score enough points. 16 points on the road in that environment is not going to get it done, and we know that. So we've just got to work to get more points on the board and give our team a chance."
The 49ers and Broncos kick off on Sunday at 1:05 p.m. PT from Levi's Stadium.