Protists
Most, but not all, protists are single-celled. The primary difference between protists and monera is that protists are more complex, having a nucleus. Protists are a very diverse group of organisms. They are basically all the organisms that don't fit into the other groups.
Many protists appear to be both plant and animal. Like plants, they are green, and can create their own food. However, like animals, they have moving body parts and are able to move around their environments. You can see why scientists no longer classify living things into two kingdoms. Into which would you put these unique organisms? Some are autotrophic and can make their own food and some are heterotrophic and have to consume other organisms.
Biologists believe that ancient protists were the ancestors of plants and animals. Seaweed is a large multicellular protist. Algae also fit into this group - although confusingly, scientists put some algae in the monera kingdom as well.
Protists can reproduce asexually by splitting in two but some can reproduce sexually as well.