This stage requires you to kill and hunt down the ducks. Because the ducks are high up in the air, you will need item to help you fly:

Round 1: Pegasus and Laser Gun
Round 2: Wings and Gun
Round 3: Flying Shoe and Spear

Alternatively, you can simply drop “lava” on the ducks to instantly kill them without having to move Maxwell.

Scribblenauts Remix 7-5 Cheats Hints gallery:
7-5-1-a: Hunt Duck!
7-5-1-b: Shoot all four ducks.
7-5-1-c: Equip a jetpack to reach the duck on the cliff.