How do I get the key to the door?

Hint 1 of 7:

If you press the switch to the right of the door, you'll see that the key
temporarily appears.  All you have to do is find a way up to the key, and
you should be able to get it without any problem.

Hint 2 of 7:

There's a catapult next to the gate that will help you.

Hint 3 of 7:

A catapult can propel you up, but only if you put some kind of force on the
other end.

Hint 4 of 7:

The weight of one of the goblins might be enough, but the only problem is
that one goblin is holding the switch, and you need two other goblins to work
the catapult.

Hint 5 of 7:

So maybe you should wait until you have a third character.

Hint 6 of 7:

Get the Buffoon down by feeding him, and then position him on the catapult.

Hint 7 of 7:

Then press the button to make the key appear (W) and use the catapult (F)
to shoot the Buffoon up.  Then you have to worry about rescuing him.