Coach Nathan Brown made a surprise change to the line-up in Saturday's final round match against the St George Illawarra Dragons at Jubilee Oval.
While named at six, Mullen played at hooker for the first time in his career after a rib injury sidelined Tyler Randell.
“It was something I have wanted to have a look at for ages... but injury has prevented that,” coach Nathan Brown said after the two-point loss.
“I thought he played really, really well.
"Defensively Jarrod was great, his commitment and effort were great.
"He certainly did a lot more than what he's used to doing.
"His kicking game out of there is good... but we never really had the best chance to see him attack.
"But you can see glimpses of how good he'd be in attack out of there as well, he is very quick, he is a good athlete."
As for playing in the number nine in the future, Brown said it is something he and Mullen will need to discuss.
"It is definitely something as a club we can look at," Brown said.
"We have some good young halves coming through, and Mullo played great there today, so it does gives us some flexibility.
"That is something to discuss before pre-season starts."
