The monster in question is the image in the attached file. It only exists in the map "Grave of a wrecked ship". The bugged attack is where he spit out his tooth and it has the ability to bypass magic guard. That shark deals 1700 ish damage to me and killed me despite I have magic guard activate. If it were normal scenerio, I would've survive by having a portion of my mana tank its attack. My mage is a lv107 priest. IGN: Nagashiii, HP:1782 MP:9106
The attack itself does not bypass Magic Guard, but Shark has another ability that you probably didn't notice. It debuffs all of your buffs, Magic Guard included. There are no bugs here, I think. Just a rather special monster