A Rare Furcorn is bred the same way as a regular Furcorn, just with a smaller chance of being bred. Of course Noggin + Furcorn = Clamble, you’re combining the Earth, Plant, and Cold elements, which makes a Clamble.
Another note, it was listing all of the possible ways a Furcorn could have a chance of being bred. Almost all of those were breeding fails, though. Stick with the same combo for the common monster for the rare monster.