If there is one thing Collingwood coach Craig McRae and Geelong counterpart Chris Scott can agree upon, it's that Mullin will be stuck firmly to Nick Daicos' side in Thursday night's blockbuster AFL clash at the MCG.
That could prove pivotal as ninth-placed Geelong and eighth-placed Collingwood attempt to start their respective runs towards finals.
Geelong will be without captain Patrick Dangerfield, managed after dealing with a jarred hip, with Jack Martin returning.
But a critical figure will be Mullin, who was a Gaelic football star for Mayo before joining Geelong in 2023.
Scott revealed this week the 26-year-old had faint hopes of playing in the All-Ireland final against Kerry on the weekend.
But given it came amid a hectic schedule where Mullin had roles on St Kilda's Nasiah Wanganeen-Milera, Melbourne's Kysaiah Pickett, then Daicos, it simply wasn't possible.
Instead, Mullin - who played in All-Ireland final defeats in 2020 and 2021 - watched on from Australia as his friends claimed Mayo's first title in 75 years.
"I guess it's bittersweet for him, because he's so happy for his really close mates, it's been such a long road for them," Scott said.
"There's clearly a part of him that would have loved to have been a part of it.
"We were really open to it - it's just Friday night in Melbourne to effectively 12:30am in Ireland on Sunday night, even for us it was just a bridge too far.
"But he was in good enough shape to stay up and watch it with his Irish mates. He's very proud of them."
Scott sees Mullin as more than just a tagger in the future - pointing to Brisbane co-captain Josh Dunkley as a player who can shut down an opponent and win his own ball.
But first, Daicos awaits.
"It's hard to think that we'd do anything else," Scott said.
"... Oisin's obviously been critical to us. But I think I'm on record as saying Daicos is the best player in the comp."
Daicos, the clear Brownlow Medal favourite, has averaged 35 disposals, 5.6 clearances, 6.5 inside 50s and a goal this season and put Collingwood on his back on multiple occasions.
He is also getting better at shaking tags.
"We think we're getting better at it in terms of trying to support him around what that looks like, and he's going to another level," coach Craig McRae said.
"His running capability is like nothing I've seen, and so that's a challenge for the opposition.
"But he's at the top of his game, so I'm sure there'll be some restriction for Nick.
"We'll just sort of weigh up how much is too much for us, and we'll try to manipulate the best we can."
Collingwood regain Lachie Schultz from an ankle injury, while losing Brayden Maynard to knee surgery.
