Sickly is a green muskrat who is always seen sick. He has a blushing red nose and wears a hot water bottle on his head. His head is a lighter green than his body due to his illness. He may develop rashes at times.
Sickly usually sneezes, coughs, and blows his nose. He also has a wide range of allergies. He has been known to give other characters his illness, sometimes leading to lethal results. A regular gag involves Sickly sneezing or blowing his nose so hard that he would fly into characters and objects. His head is so hot that he may burn whoever touches it.
Sickly seems to be pretty clumsy when it comes to his illness. When Sickly sneezes, it sometimes causes him to fall backwards and lead to the deaths of himself and others.
Sickly does not really care when he sneezes on others. He seems to be mildly stupid, even to the point of not even knowing when he sneezes on others. Sickly is usually calm and relaxed. A mysterious thing about Sickly is that it is unknown what kind of illnesses he has (some fans have debated on him having flu and colds, among others).