As @gr5org suggested, the usual trick with Marvin is to print more than one at a time (or print something else the same height, as suggested, like a 10mm “tower”). Have you tried this?
I haven’t read the other comments yet, so I’m not sure if this is mentioned. Your layer height is very low. A nozzle diameter of 0.2 or 0.15 mm is necessary for this layer height.
Believe it or not the UM2 and UM3 can do .06mm layer heights with a .4mm nozzle. I recommend people go a bit thicker. I’ve never had the patience for a 50 hour print. But you can do it. You can’t really go much thinner with a .4mm nozzle though because… well I’m not sure why. I think the quality starts to get worse again thinner than .06.
I don’t have an UM2 or 3 but with other 0.4mm nozzles when I pushed the layer height too low, I started getting very rough surface texture and seemingly over extrusion. The nozzle could heat up the previous layer since the distance is only 0.06 mm.
I would experiment with only 2 marvins (to speed up the experiments) and go a little thicker layer and go a little slower print speed: 25mm/sec. Overall it should be faster with the thicker layers even though the head moves slower. Those overhangs are tricky. You can also go even lower in temperature.
Are you using cura 2.X to slice? Your entire remaining issue might be that the infill speed is too fast. When you have a fast infill speed and then switch to the outer layer the pressure is a bit too high and it overextrudes sometimes for a bit.
You can also print just the top half of a marvin to help concentrate on the spots you care about so you can do more experiments in less time (testing .06 versus .08 versus .1 layer height - testing 195 versus 190 versus 185 verus 180C - testing 30mm/sec versus 25mm/sec). Printing smaller prints means you can do more experiments in the same amount of time which means you learn more faster.
