Using your Bulldozers, carefully push the boulders in front of the Scorpions to block them off. Once they can't reach you, grab the plans for the Frog to the northeast, then use the pile of green bricks and an energy brick to build a Frog. Using the Frog, traverse the water to grab the Duck plans to the south, making sure to avoid the Watercrab. Once you have the plans for the Duck, feel free to return the Frog back to the bulldozers, as you'll need it for the Bonus Goal. Take apart one of your Bulldozers, build a Duck, and traverse carefully around the Watercrab to reach the goal.
If you decided to have your Frog return, this goal will be especially easy to get. Simply have your Frog stand in a certain spot between the boulders on the far left, and you will get both goals at the same time.