Liam's hatred of platypus started at a young age. In Australia, his mother was distracted by a platypus, leaving Liam and his stroller to roll away.
After Perry the Platypus is sent to Danville Botanical Gardens, Doofenshmirtz reveals to have hired Liam to trap him. This quickly gets out of hand when Liam threatens to make a trophy out of Perry, and Doofenshmirtz as well.
The two foes work together to defeat Liam, avoiding his boomerangs. He proves to be one of the few villains who stand a fair fight against Perry. He is ultimately stopped by Doofenshmirtz and some groundskeepers.