Several religions across the multiverse believe a soul can be tainted or polluted by bad behaviour (or even bad thoughts), though not all religions with a concept of sin necessarily include the idea of a distinct soul.
Religions with evil beings (eg demons) and religions that believe souls can be detached from the body may both include beliefs about people 'selling' their souls to someone else. The soul is sometimes given away immediately, sometimes promised as payment after the seller's death.
Other religions teach that the soul is something earned, or given as a gift later in life or upon death.
A few religions teach that the souls of sufficiently good or evil people may become angels or demons after their death. (Note that others believe angels and demons are separate types of life form altogether, not made from dead animals.)
Instarrian religions, the 'soul' is equated to a 'destiny'. More about souls on Instar
Evil is occaionally equated to the absence of, or a deficiency in, a person's soul, generally meaning 'soul' in the sense of something that gives people empathy or makes them want to behave in a good way.
Some people think most animals have no soul and may use this to justify thinking of their own species as completely separate from all other species. (Others suggest that anyone who would believe this sort of thing about animals is soulless themselves.)
Soullessness is a term occasionally used to describe individuals with the innocent? syndrome. (Usage note for travellers: the term 'soulless' should be avoided in most societies because it is usually highly insulting to suggest a creature with a mental illness is less of a 'person' than anyone else.)
In beliefs where the soul leaves the body after death, vampires, 'undead' and other revenants (reanimated dead people) are often believed to have no soul.
Some understandings of mindbonds involve a connection created between two souls.