Peanut is extremely weak and sickly; even the act of sitting up too fast or walking for a few minutes can leave him out of breath. He is also prone to fainting; when Charmander first met him, Peanut was passed out in the middle of a Beedrill nest. Charmander is often annoyed with Peanut's "Wimpiness".
Peanut first appears in Charmander's Peanut, where he and Charmander are trying to find the legendary Fruit of Great Strength. However, due to Peanut's misreading of a map, they never do find it.
Peanut's sickliness is caused by a concentration of dark aura, as is revealed by Plum and Chansey.