Run each creature down a branching yes/no key into the right kingdom and class, then try building a key of your own.
In Sort mode you place each organism into a group by answering the key's yes/no questions about its traits. In Build mode you become the taxonomist: author an ordered list of yes/no rules that correctly separates every creature into its group. Get them all right to clear the round.
Classify is a taxonomy puzzle that teaches dichotomous keys and biological classification, training the logic of sorting living things.
Sorting organisms by answering a key's yes/no questions is a single-access key — the dichotomous key used in the field.
Switching to Build mode and authoring the key yourself is the original second half.
Writing one is far harder than following one, and that is the point. A good key asks the question that splits the remaining group most evenly, using characters that are actually observable — which is where amateur keys fail, by asking about features you cannot see without a microscope.
Classify is an original taxonomy puzzle that teaches dichotomous keys and biological classification. It's free to play in your browser with nothing to install.