Wicked 4 is improved to 1 climber, 1 bomber, 16 builders, and 1 basher. The 16-builder solution and the 1-climber solution differ in the way that they handle the left side of the level.
The 16-builder solution has the lower-left group build through the stairway to the left of the entrance. One lemming then builds from this stairway to the red blocks underneath the top left entrance. This uses up 10 builders, and the other 6 are used on the right side.
The 1-climber solution involves building over each of the four water pools so that the lower left group joins the lower right group. This allows the two groups to share a climber, but it also requires an extra floater and builder for the top left group (their fall is too far by one pixel).