Splash Damage is the 6 star urgent quest for Moga Village. All you have to do is kill a Plesioth, a returning monster from the older Monster Hunter games. Plesioth is basically a giant shark or fish, and he is very quick but overall not too bad. Unfortunately, he does hit like a truck though so you should bring lots of potions and healing items.
I used a Lagiacrus set upgraded to level 8 with Flamestorm dual blades.
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