Just like their original counterpart, they were voiced by Dee Bradley Baker.
Cheer Up Candace
In the episode, several robotic platypuses were created (with the likeness of Perry the Platypus) by Heinz Doofenshmirtz as part of his plan to tarnish Perry's reputation as a secret agent. As such, the robots were programmed to commit crimes throughout Danville, forcing Perry to go on the run from the law.
However, Perry soon learns about Doof's plan and confronted him and the robots for this. Perry then fought against the clones, effectively smashing them one by one. Perry then leaped onto a lounge chair, flinging one of the robots (Jerry the Platypus) at the "reverse" button of the machine that created the robots and causing it to suck them and Doofenshmirtz into it. This causes the machine to explode, destroying all the robots, though Doofenshmirtz survived the incident.
Invasion of the Evil Platypus Clones
In this story, Phineas and Ferb were having a campout with their friends in the backyard reading Halloween stories. They eventually come upon a story that warns that spilling grape juice on a platypus will cause it to duplicate and form a evil platypus clone. Wanting to see if the story is true, Buford pours some grape juice on Phineas and Ferb's pet platypus Perry, inadvertently creating a purple clone of Perry.
Though it would've appeared that the purple clone seems harmless at first, he starts to get feral and steals the grape juice, eventually creating more evil clones of himself. Realizing that the evil platypus clones will be running amok throughout Danville and cause chaos, the kids decided to take action by eliminating them all; even Perry finds them to be more dangerous than Doofenshmirtz, though he is unable to do anything about it as he cannot expose his identity to the kids. They eventually found out that using combined soap and water will do the trick, so they used packs of soap and water to wipe out several of the evil platypus clones.
Unfortunately, there are too many of the clones and the kids end up being surrounded by them in a grape juice factory. Luckily, a cowboy named Rusty Britches came to the rescue by turning on one of the factory's pipelines, releasing massive amounts of soap and water through the sprinklers, killing all of the remaining evil platypus clones for good.