After they get a book of witchcraft from Carbonek the librarian, the goblins head farther into the castle.
How to Clear Gobliiins Level 20
Have 
Hooter/Ignatius use magic on the shield in the base of the
stone platform next to the giant. A lever comes up out of the ground.
Have 
Bobo/Asgard punch it to make a ladder come down from the
statue on the platform.
Have Hooter/Ignatius use magic on the cork in the giant's ear.
Then have 
Dwayne/Oups use the book of witchcraft on the giant's
ear.
Then change the cursor to an open hand.
Click inside of the round tower in the upper-left of the screen to pick up the
object that is partly visible in the tower doorway. You will get some bait.
Have Dwayne/Oups pick up the bowl in the upper-right tower.
He will leave the fish in place of the bowl.
Then have him place the bowl on the ground to the right of the lever, where
the giant's tears fell earlier. Then click the round tower in the upper
left of the screen to get the witchcraft book again,
and read the book of witchcraft to the giant
again. Then pick up the bowl to get the giant's tears. Use the giant's tears
on the monster that appeared in the upper-right tower. It will turn into a
slingshot. Pick it up.
This completes the level. Click the flashing "Go" in the door in the upper-left. Make a note of the code in the bottom-left of the screen ( ), then click anywhere to continue to the next level, The Writer's Castle, Part 2.