After the goblins get an hourglass from Tom, they can enter the castle to look for the Prince.
Get Mayonnaise
Have 
Fingus take the mayonnaise that is in the middle of the
bottom of the screen.
Get Chewing Gum
Have Fingus stand near Stalopicus, who is sitting near
the cupboard with the fish markings on it. Switch to 
Winkle and click on Rustik, who is sitting near the barrel on the left side of the
screen. When Stalopicus opens his mouth, switch to Fingus
and click in his mouth to get the chewing gum.
Get the Imprint
Have Fingus use the chewing gum on the cupboard to get an
imprint.
Get the Knife
Have Winkle stand to the left of Gromelon, who is holding a
knife and is to the left of the center of the room.
Then switch to Fingus, then click to the left of the skull
in the upper-middle part of the screen. After he jumps off the roof,
have him walk one step to the
right, then have him use the
mayonnaise one step to the left so that it is where he landed when he jumped
down from the roof. He will leave it on the ground in that spot. Then click
to the left of the skull again, and have Winkle click the
sword that is next to Gromelon.
Get the Mayonnaise Again
Be sure to pick up the mayonnaise again before you continue.
Go to the Forge
That is all you can do here for now, so just move the cursor to the bottom-left of the screen until it turns into a door icon, and click to go to the forge, or move the mouse to the top of the screen and choose the wooden sign, then click Forge to go to the forge.