La madrastra de Natalie resultó ser tan malvada como cualquier madrastra de los cuentos de hadas.Natalie's stepmother turned out to be just as wicked as any fairy-tale stepmother.
This means that the noun can be masculine or feminine, depending on the gender of person it refers to (e.g. el doctor, la doctora).
La hermana de Laura es una malvada que la estafó robándole la herencia de sus padres.Laura's sister is an evil woman who cheated her out of their parents' inheritance.
malvados
A plural noun indicates that there is more than one person, place, thing, or idea.
El manuscrito dice que los dioses castigarán a los malvados y llenarán de recompensas a los virtuosos.The manuscript says that the gods will punish the wicked and heap rewards on the virtuous.