Item locations for Fatale's quest, "Fatale's Secret".
Three Headed Acorn
Location: courtyard - east side
At the east side of the courtyard (the side with the large portculis), the acorn is on the ground near the bottom of the long stone steps that lead up into the fort.
Beetle Eggs (x2)
Locations: courtyard - above the skappbeetle pen, courtyard - watchtower
For the first lot of eggs, climb onto the cannon next to where Silas keeps his skappbeetles, and then up onto the nearby roof to find them.
For the second lot of eggs, take the steps near Silas up into the watchtower and make your way up the spiral staircase to the top. The eggs are in the window next to the chest.
Locations: courtyard - secret passage, sewers - torture room, sewers - dead spider alcove
From the cell next to Gusto and Fatale, push the barrel aside and take the secret tunnel. Head straight foward until you can turn left, and you'll find the mushroom.
In the sewer torture room, the mushroom is in the hanging cage containing the skeleton. Just throw a stick or a bottle at the cage to make it drop to the floor.
The last mushroom is in the cobweb covered alcove with the dead spider (this is in the same cavern that contains the entrance to the torture room, Climb some rubble and burn the webs with a candle to get to the mushroom.