Big Momma Trophy
Kill the Queen of the UnderworldStory-related and cannot be missed.
This trophy is for defeating the Queen of the Underworld, the final boss of Act 1.
During Act I, you'll search for the cause of mutated villagers and set out to put an end to whatever disease is causing it. Eventually you'll be following the blue sphere (on radar or via Aura Sense) to the next objective, jumping from boat to boat (remember, don't fall in the water), until you reach a boat with a voodoo ritual left behind. A cutscene will occur and the boss will emerge from the water and you'll find yourself face to face with the Queen of the Underworld, AKA the mother of all insect monsters.
When the boss dies, you'll get a short cutscene and the trophy will pop. For more on the boss and tips for fighting her, see below [Spoiler Warning!]:
She can be surprisingly tough. There will be random mutated monsters around and personally I suggest leaving them so you can use them to replenish your health during the boss fight if need be. They won't bother you during the fight anyway as you'll be far enough away from them. The best way to kill her is, using your Blood Rage, attack one of her legs until she falls over. Once she does, attack her torso until her leg grows back and she stands back up. If needed, rinse and repeat as many times as needed until she dies but you should be able to kill her in one full Blood Rage attack in Normal mode.
Here's a video showing how to kill her: