Mullens has passed for 1,479 yards with nine touchdowns and six interceptions in five starts. He has passed for 746 yards with four touchdowns, two interceptions, and a passer rating of 98.1 over the past two weeks.
Mullens credits much of that success to the coaching staff's ability to prepare him for each game and work to his strengths.
"I've really enjoyed learning and playing in Kyle's system since I got here," Mullens told reporters on Wednesday. "They really do a great job of [scheming and getting players open], disguising different looks every week about what we're trying to do, and just giving me good opportunities to sit in the pocket, progress, and make quick decisions.
"So, a lot of the success is definitely a credit to the coaches, 100 percent."
Mullens says he was aware of Shanahan's reputation before signing with the 49ers as an undrafted free agent in 2017. His two offseasons learning the coach's system was a significant contributor to his current success. Now, Mullens is using his opportunity to prove he can be Jimmy Garoppolo's backup next season.
"I understand my limitations," Mullens said. "I understand what strengths I have, and the strengths that I don't have. I understand how the process worked. I never expected to be drafted, to be honest. And if I did, it would have been really cool. I'm just glad I got my opportunity."
Mullens has proven he can make quick decisions and handle whatever game plan Shanahan and company throw at him. So, what are his limitations?
"If I showed up at the combine, I wouldn't be the biggest, fastest, or the strongest," Mullens answered. "I guess evaluators put a lot of thought into that. It's just part of the deal. I just always thought, 'This is what I've got, and it's my job maximize it.' That's what I try to do every day."
On Sunday, Mullens will make his second start over the past three weeks against the Seattle Seahawks. Despite throwing for over 400 yards against them on December 2, his 49ers were routed by a score of 43-16. Mullens will have the Seahawks at home this week and hopes for a different result.
"There's some recall going back to things we did against Seattle," Mullens said as he explained the process of preparing for an opponent he so recently faced. "We can look at how we did the first time, what we can do better, and what things worked, and what didn't. So, definitely some recall going back to the first matchup, and definitely looking forward to this week, seeing them again."