That is a moth of some type. Moth antennae are either filamentous or feathered. Butterfly antennae are clubbed.

Insects grow in stages in a process called molting where the previous exoskeleton is shed. There is usually more than one instar (stage) occurring in the larval or nymphal stages. Each stage becomes progressively larger. The advanced insects go through a single, motionless pupal stage. Then the fully formed, sexually mature, often winged adult emerges from the pupa. That's it. There are no stages for insects after the adult.

Moths and butterflies go through a complete metamorphosis, which is also called holometabolism, meaning that they change dramatically between egg, larvae, pupa, to adult.

Less advanced insects, like aphids, go through a less dramatic metamorphosis, where the most noticeable difference between nymph and adult is the presence of wings. There is no pupal stage. This type of metamorphosis is called hemimetabolism.

More primitive insects like silverfish do not change much at all, except for becoming sexually mature. This type of metamorphosis is called ametabolism.

Molting is controlled by many factors. One of the factors is a chemical prohormone known as ecdysone. Imbalances in this chemical can cause malformed insects. I've seen malformed wings in butterflies before. You could be looking at what is essentially a type of "birth" defect.

Also, when a butterfly or moth emerges from its pupa the wings are the last appendage to be formed and are formed by the insect expanding its wings with air brought in through its spiracles. If a moth or butterfly is interupted at this point its wings may not fully develop.