So. Doctor Doom has built a castle which, in order to get inside, you need to break down all its walls. So the Hulk breaks down the first wall rather easily. Drax breaks down the second wall with a little more difficulty, but still with very little effort. The Thing shatters the third wall with impressive strength after weakening it first.
And for the fourth wall, Deadpool simply looks up.
” Am I supposed to be the punchline of this joke? “