Miner Magnus is a subject of Miscellania, whom you need support from in Throne of Miscellania. He is located in the coal mine. When mining at the mine of Miscellania, all of your ores (and gems) are given by you to Miner Magnus, which will, if Throne of Miscellania is completed, raise your popularity in your kingdom by .8% percent, or higher if the Fremennik Hard Tasks are completed. Strangely, this NPC uses the old mining animation and will continue to mine from the rock even if a player mines the ore from it and gives it to Miner Magnus. Miner Magnus is one of four residents whom you can assist to gain favour; the other three are Gardener Gunnhild, Lumberjack Leif, and Fisherman Frodi.
Miner Magnus is Latin for Big Miner. This is might be a nickname (like Big Dave). Magnus is also a Scandinavian forename, and as such his given name fits with the Scandinavian theme of the Fremennik province.
Miner Magnus appears to be a terrible miner, as no matter how long you watch, he will never gather together even a single ore without your help.
If you mine the coal rock that Miner Magnus perpetually works on, he will continue mining an empty rock.
Before the major graphical update, Miner Magnus had a huge belly, now, it is not as big.
Sometime between December of 2011 and February of 2012, the rock formation of the coal next to him changed. It is yet unknown if this has a distinct underlying purpose.