The Plantimal was a mutant creature created by Mixmaster. This creature was the most extreme mixing of DNA accomplished by the chemical, as it was cross-kingdom, i.e. a mixture of both plant and animal.
Back when the Mixmaster compound was still in the lab it found its way into the botanical division. Though all of the plants had been dead for years Mixmaster was still able to acquire their DNA. This particular lifeform's DNA was primarily a squash or gourd, but inherited the powerful digestive acid of a pitcher plant and the contractiveness of a venus flytrap. It also had a rudimentary circulatory and nervous system, likely from a lizard, allowing it to grow very large.
The plant colonized an isolated area in the valley and remained mostly undisturbed (20-30 years) until it began to spread out along the valley floor growing pressure pads here and there that released a powerful acid onto any animal that stepped on them and then absorbed the nutrients from the remains. The plant was eventually discovered when it attacked a pair of scientists that came with a government team who where there studying Mixmaster's effects on the local environment. The situation, while already dangerous, became a full blown crisis. The plant needed to be killed before it experienced seed-ejection meaning that the plant would spread everywhere. Burt and the gang teamed up with the scientists to create a powerful pesticide that would kill the plant and set out to kill the plant by injecting it's trunk with it which would spread the poison throughout the whole organism. This was far easier than first thought when the job was given to Larry who's shear dumb luck allowed him to walk through the plant area without setting off the pads. Eventually using a hot-air ballon, Tyler Reed is able to reach the trunk and inject the poison, but one pod managed to eject its seeds as it died, but Larry was able to cover them with his coat. The seeds were then destroyed, but one survived and flew out of his car as he left, but was crushed by Burt before it could do anything.
It's life cycle starts with a seed that resembles those of dandelions, which there are about a million in each flower. They float through the air, and they land in a spot of soil, where they grow into the acid sacs.
The Juvenile stage is the acid sacs, which have Venus Fly Trap DNA in them, they shoot out the acid at any thing that vibrates. The acid burns you to the bone in less than ten seconds, but the victim dies before they are burned.
The third stage of it's life cycle is maturity, when the flowers have began growing out of the acids sacks. In the episode, there was about 300 or 400 of the flowers.
The final stage is Reproductive, in which the plants begin to rattle and shake when the temperature reaches 81 degrees. The flowers then spray out about a million seeds each, then the flowers die, and the seeds grow through the life cycle too.
- All in all, the Plantimal could easily be considered the most dangerous of all the creatures to appear in the show. Since it could've easily spread itself across the country and possibly even the world if it hadn't been stopped in time.