Fishing MMM is easy. Just enter talk to the moblin to enter like all MMM. Then talk to the one inside to start it.
Go to fishing spot and fish.
You can hold 1 large fish and I think 3 small fish idk it tells you if you want to get instructions. After you get some you turn them into the other moblin at the start who keeps track of your points.
Birds spawn if it goes on long enough and if you get to close to them they will eat your catches. Also monsters you fish up might too so pay close attention to what you reel up. Most monsters will stay till they can eat something. Some will leave if you run enough and I think the leech you can actually turn in lol. While they are out you have gravity effect.
As for fishing I only use the first 2 ponds and always win way ahead of time except that one time got a glitch lol. You can tell if a pond still has fish in it and about how much by the amount of sparkles it gives off. 0 being none 3 being full. If the other guys don't go to the first pond you can actually get all you need just from it rather quickly
Pond #1 (the one right in front at the start) Sinking Minnow Giant Catfish. Message should be something like !!! and something negative like Terrible feeling or You're positive you don't have enough skill to reel this in
Pond #2 (the first on after taking the first left) Shrimp Lure. Black Eel !, Monke-onke !!! Messages should be Terrible feeling, or You're positive you don't have enough skill to reel this in as well.
Seriously by far the easiest MMM. It's actually what I use to build up marbles now. Oh and don't use salinity shift as it changed everything to salt water