Coulson struck on 25 minutes to equalise following Peter Bore's opening goal for the hosts, managed by ex-Reds academy boss Stuart Watkiss.
This was to be the only time the Reds would hit the net though, with Grimsby running out 4-1 winners. Further goals from Danny North, Andy Taylor and a Mark McDermott penalty.
Reds assistant manager Ryan Kidd was delighted with Coulson's return and told www.barnsleyfc.co.uk:
"We were really, really pleased with Michael and he played for more than 70 minutes but could have probably done the whole game. We were always going to give him that but he scored a good goal and looked sharp. He also had three or four shots and stung the keepers' hands a couple of times so it was great to see. He is still a long way off being ready for the first team but it is great to have him back.
"We are all absolutely delighted with his first game. He suffered no ill effects and looked strong. It went better than we could have expected really and Michael could have looked very rusty out there. He did not and was sharp and lively. He now needs his match sharpness back because mentally he looked fine. It was a difficult afternoon for us but we are delighted with Michael. He had a massive spring in his step when he came in to pick up his kit and I think just pulling on a Barnsley shirt again is a massive thing for him. Being out for six months is a very lonely time for a footballer when everybody else is out training and playing games.
"Michael started the game well and led the line for us at times. He looked mentally very sharp and a lot of that has to go down to the physios and to Dave Kelly, who has worked with him through most afternoons. He now needs four or five reserve team games to get his match sharpness back".
He added: "We had a very, very young side out at Grimsby and they were up against some senior players with a lot of experience. They had a little too much knowhow for us at times and we were a little niaive in defence.
"The lads have to learn from that and improve. It is something the will have to take on board quickly because we want them to be better than that. Having said that there were some bright spots at times".
Reds Line-Up: Letheren, Tienan, Reffin, Branson, Grundy, Heslop, Hibbert, Butterfield, Coulson, Noble-Lazarus, Taylor.
Subs: Fearnehough, Bennett, Watts, Crapper, Mellor.