I found my mosa near a Florida- looking edge on edge of the middle right of the map. I brought a Ramshackle Crossbow and 150 Tranquizer Arrows (jelly arrows) and took it out with only 49. Used a soothing balm (X10) and fed it fish meat cuz my Ichy ate all my good food. It woke up at 47%, so I headed back to base to try again. This time, I used my same tool, and the Mosa still had the soothing balm on it so I was like 'yay'. I tranq it out again with 307 Bio Toxins and fed it prime fish meat (27% per bite) and it worked! Mine looks like a legit killer goldfish. I hope this helps!