Gobul is one of the scarier monsters for me in Monster Hunter. I just wanted to run away as fast as I could whenever I faced it (or rather, swim away), and when I finally did beat it, I absolutely refused to hunt it again for more materials. Good thing I had a bowgun so I didn't have to get too close to it and possibly crap my pants...
The scary thing about underwater battles is that it is pretty much always more of the monster's territory than yours. Something like Royal Ludroth was fairly relaxing to fight on land, but underwater it looked much larger and terrifying, and it was much faster too.